Probably pretty unlikely that your increase in efficiency is related to mash time; but there are way too many variables to get from here to there.
You ARE asking a good question and moving your thought processes in a good direction, though.
Theoretical information regarding your question: There ARE many variables involved in mashing and determining how long to mash but the most significant ones are the total diastatic power of the mash, time and whether you recirculate or not; water-to-grist ratio and temp profile are also important factors.
Practical advice in this area:
1. Start performing an iodine test during your mash to get a good feel for how conversion is proceeding so you know where you are at (no calculations required)
2. Start calculating each mash's total diastatic power and use that as a calculated estimate for how long you will need to mash -double check your calculations are panning out in practice with the iodine test
3. Think about what you want out of the mash and further tweak your mash length to accomplish those goals (if you want more body, a shorter mash in addition to higher temps can be useful (within reason-you need to do the calculation and go from there), if you really want to dry a beer out to finish super dry you'll want an upward infusion mash and go a bit longer to really get down to mostly simple sugars
Iodine Test: Buy an eye-dropper container of iodine at a local pharmacy -pull a small sample of of wort (you want clear liquid and not grain husk material; filter through a papertowl if you get chunks) then add 2 or 3 drops of wort to the sample -you want a white background so that you can observe the color change. Early in the mash where there are large amounts of starch the iodine will turn the solution quickly dark black, as the mash progresses this will turn to dark bluish, to red/copper and eventually it will just look like iodine in water and dissapate without color change. The redish tones indicate large sugars but that most starches have been broken apart into medium molecular weight sugars. Iodine color-no color change means that you've really gotten rid of the starch and mega-sugar molecules and probably have a pretty typical wort sugar blend (majority maltose, with some mono and and bi glycerides and some larger unfermentable sugars). -This doesn't mean that you're done if you're going for a very fermentable wort- keep it going another 10 15 min after this because the test doesn't tell you whether you're dealing with simple or complex (unfermentable sugars) so you want those unfermentable sugars to be broken down to the maltose size or smaller.
To calculate the diastatic power of your mash:
1. Pull a malt report / do an internet query to find the diastatic power of each and every malt / adjunct in your grist (be specific, don't use generic estimates for things like "pale malt" or "lager malt", you want an estimate from your particular maltster as there is a surprising lack of standardization in time and temp processing; floor malted malts often have lower DPs, too. Ideally you want a malt report because the particular variety of malt and growing seasons matter, too. In general the higher the protein, the higher the DP; the higher the extract potential %, the lower the DP.
-Highly roasted malts, crystal/caramal malts, adjuncts and all unmalted grains will have 0 DP. Basemalts can vary from over 100 DP for 2 row, 6 row and many lager and pilsner malts down to 40-60 for some munich and MO pale malts. (You'll want to convert all diastatic power numbers from the maltsters to a common unit- I like degrees Lintner as the Germans use their own system so plug their malt reports into an online conversion calculator / your brewing tool of choice.
2. Figure out the % of your mash that each grain represents and then take the DP of each malt and multiply it by the % that that grain makes of the total mash
3. Add all of the numbers from #2 together and divide by the total number of grains in the mash/grist - this will give you the total diastatic power of the mash
-The classical advice is that a diastatic power of 30-40 Lintner is the minimum required for conversion (all starch gone / pass the iodine test) within an hour, but in practice at homebrew scales, I've found that that's a bit too optimistic and it seems to take at least 45 L to complete conversion in a single, unstirred, unrecirculated mash in 60 min at typical middle-of-the-road mash temps.
If the DP of your mash is 100 or higher, you can definitely dramatically decrease your mash time and you'll find that you can pass the iodine test very quickly. Recirculated mashes also convert faster, so that's another significant factor, I decrease my mash time by 10-15 minutes if I'm recirculating otherwise I always end up with an overly thin tasting/feeling wort. In theory if a 45 L mash can finish conversion in 60 minutes then a 90L mash can finish conversion in 30 minutes. Again, that's just when starches are gone and doesn't involve extra time for breaking down those last few freed huge sugar molecules into something fermentable so make sure you wait a bit longer if you're going for a dry beer/ highly fermentable wort.
American 2 row malts are often in the 120-140L range so if you have a very light california IPA recipe that is 100% 2 row then you have a whole mash DP of 120-140L and you're going to complete conversion VERY quickly, especially if you're a HERMS or RIMS user. On the opposite end of the spectrum if you're doing a traditional 100% Munich malt bock you'll have a very slow conversion and if you take a sterotypical american home brew recipe with crazy amounts of speciality malts (which all provide 0 diastatic power) and you are using a floor malted English Marris Otter basemalt from a maltster who lets their basemalts kiln a little too long, you could end up with a mash that has no hope of finishing within 60 minutes and may possibly never convert.
-People get in REAL trouble when they try and recreate historical recipes with modern malts at teh same percentages -historical porters are famous for never converting because the brewers don't understand that historical Amber malt was diastatic and could self-convert but modern day Amber malt has NO diastatic power left.
Random related trivia:
All malted grains start out with diastatic power and generally loads of it, it is the heat and time at heat that starts degrading the diastatic enzymes as the kilning /roasting part of malting progresses; the longer and higher they're kilned the less diastatic power you end up with. -This is why a you can start with the exact same variety of barley from the same lot from a particular farmer (which all will start with the same diastatic power after the early malting stages) and you'll end up with different DPs for your 2 row malt (lowest temp and least time at high temps), Lager/Pilsner malt (very similar lowest temp, lowest time kilning profiles), Pale malt (longer time at the kilning temp), and Munich malts -higher temps longer time. Then between Light Munich and Dark Munich you normally move between a low amount of diastatic power (30-45 for light) to no diastatic power or <30 for dark Munich. -A malt that has less than 30 or 35 DP can't convert itself so don't ever try to make a 100% Dark Munich Malt bock -it'll never convert and you'll end up with a glass of starch water.
Adam
