What temp range do you need for mice to breed and how can one regulate the temps in a rubbermaid tub?

I recently moved my 1.2 mice into a tub with similar proportions to a 10gal tank, but with more floor space. The entire center of the lid is window screen and I placed adhesive felt to the outsides of each side and most of the back (ran out). The thermometer in there says 73.

I have these three mice for breeding, and have owned them since late August, but nothing is happening. True, I got them from my feeder supplier as 'adults' where they are separated by size not age, so they were all together in a trough tub with many others. Could they be too old? What would be the best way to get a small breeder group going?