How long should my bees stay in the nuc?

I get that and a similar question. When can I add a super?  a lot. The standard answer is when the bees fill all of the gaps between the frames. But that really isn't what people want to know. We want numbers, weeks, days, months, how long? So we'll do some math. Things will be different depending on what type nuc you have. If you bought a commercial nuc, you'll already have a laying queen and it should be close to full of bees. In this case it will probably just be a week or two. Might even directly put them in a full sized box. But what about splits? You'll need to wait for your queen to start laying, and then for enough brood to cover the frames. It takes about 1200 bees to cover a deep frame, around 800 for a medium. So to fill the gap you need about 2000 bees. A good queen can lay up to 2000 eggs a day but more typically 1200-1500. There will also be a daily attrition of several hundred. So in reality we can expect daily increases of 500 - 700 bees. This starts after our queen begins to lay. So if you have a walk away type split, one with no queen but suitable larvae to make a queen. It will be 12 days before any queen can come out, then 10 days to mate. We won't see brood for 21 days after she begins laying, then another 12-15 days to get the numbers up. So for a new nuc, walk away split, expect them to be in that box for 2 months. If you start with an unmated queen you can subtract 12-15 days, and a mated queen 22-25 days.  Using theses same formulas we can make some good guesses for when to add the super. If I look in my 8 frame box and they cover the gaps of 5, I need another 6000 bees, so about 10 days, or 3 1/2 days for every space that isn't filled.