Question on BS Mash Schedule

When doing a stepped mash, using BrewSmith as a guideline, a sample step may be the Sacchraification Rest that says "Heat to 158.0F over 15 min" , followed by "Hold mash at 158.0 for 30 Min".

I assume this means an overall step time of 45 minutes.

So, I have a couple questions
1) If you raise the temp (steam) to 158 in 5 minutes, do you start the next step (hold) at that time?

2)If it takes longer (20min) to reach that temp, do you wait until the temp before starting the hold?

3) Does it really matter, other than reducing the brew day, if you are 10-15 minutes over on a mash step?

Just wondering here.

1.) Yes. Once you've reached your target mash step temp, you hold.

2.) Yes. See #1.

3.) Depends on the DP of the grain and how far away from your target rest you are in temp.

For example;

Grain has varying DP or diastatic power, that is the concentration of enzymes available to convert starches. The higher the DP the quicker the grain can self convert or the more adjuncts the grain can handle to convert.

The lower the DP the more time that is needed for the grain to self convert.

Most mashes run 60 minutes at a minimum. This is usually enough time even for grain with very low DP and sometime it is nearly twice the amount of time a grain with a high DP needs. Hence the starch conversion tests using Iodine.

So, time in the rest does matter depending on the grain.

The number between rests is usually reffered to as a Rise time and, IIRC, is factored into the timeline on the BS BrewSheet. Once you have learned your system you will be able to dial this in to a number that matches actual times.

As a side note, 158 is really more of a "dextrin" rest than a saccharification rest.

That 15 minutes of rise time can make a difference. Whether it's intended or if the software "knows" it, is another matter. As an example... If you're rising from a "Protein/Saccharification" rest at 131dF and you raise it to 158dF for your dextrin rest, it will make a difference in the amount of fermentable sugars in the wort. The longer you take to go from 131 to 158, the higher the proportion of fermentable sugars will be in the wort... because the mash has more time for conversion in the optimum saccharification range (mid-high 140s to low 150s). It may not be a huge difference, but it's worth considering.