Those look like 2.5-3 gal pots, is that close? If so, they would probably benefit greatly from a transplant now to a bigger pot. It'll give them a few more weeks to grow their root system and settle in before flowering starts.
Don't use tin foil, you may end up burning up your plants and if you're not medical (I assumed you are) then it's a red flag. I'd either spray paint the pots white (don't get any on your plants or in the soil!) or wrap them with standard white paper or tyvek or something.
Of course the best thing you could do would be to get them in the ground asap.