Fermentation Temp Length

i'm going to use a swamp cooler for my next batch to control the temperature of the beer.

im wondering how long do i have to keep the fermentation bucket at 65-70 degrees? can i stop after primary fermentation is done and let it ferment in room temp for secondary or do i have to keep it at 65 -70 degrees until it is bottled?

I don't have any hard rules about when I allow myself to become more lax about the ferm temps, but here are some of the things I look for:

-less bubbling
-decreasing krausen
-less requirement for cooling
-less chunks floating around
-a layer of yeast trub beginning to settle

For an average gravity beer with a proper amount of yeast pitched, all these factors mean I wait 2-3 days until adjusting temps. Until then, I try to keep it in the sweet spot. I don't really take gravity readings during fermentation, but I would guess all of these signs indicate that fermentation is at least 50% complete, and probably closer to 75%.

I also make sure that there still is some yeast activity going on when I stop controlling temps, because I want the temp to slightly raise. This keeps the yeast active and they clean up any by products and fully attenuate.

The most crucial time frame is the first week and first few days when the yeast are at full force and producing the majority of by-products. This would include the by-products with undesireable flavors from hot fermentations like fusel alcohols. Generally a week out the yeast are much more calm and a couple degrees warmer is not so crucial like you mentioned.
However, remember that it's not the temperature of the water in the swamp bath but the temperature of the fermenting beer that is important and these vary quite a bit.

Oops, pressed Post before I was done.

You DEFINITELY don't need to maintain those temps up until bottling. I mean, you may not want the beer to get in the 90s, but room temp is fine.

And nice work on taking the plunge into temp control - it improved my beer by leaps and bounds. Taking care of your yeast is waaaaay more important than picking out the perfect grain bill or planning your hops to the gram. In fact, it's the most important thing in brewing after sanitization.

I assume we are talking about an ale yeast.

The first 2-4 days are the most critical to keep it cool and under control. After 4 days you can let it warm toward the high end of the target temp. The warming will help the yeast stay active, clean up off flavors and fully attenuate the wort. After 7-10 day it should be done. You should bottle it. It's OK to leave it in the fermenter. Ideally you would cold condition it but it's not gonna hurt it if things go a it warm. Warm is OK at this stage but if the temps get super high (80+) the yeast will die and you could have some autolysis.

Yeah i finally figured why my beer wasnt taste as great as it could have been. it all had to do because of temperature control. for some reason i usually brew during the summer which is a pretty difficult time to brew good beer.
i've actually practiced controllin the temps by filling my bucket with water and puttin it in the swamp cooler and placing a thermometer inside the bucket. im stoked gonna brew a Hef today.