With corns, the rule of 3 is what I follow for girls: 3 years, 3 feet, 300 grams minimum of ALL 3. The biggest risk you run with breeding lower is them double clutching and then they lose too much to bounce back. Honestly, I've never bred a smaller boy like that but I would be careful about it if he's noticeably smaller. There is a reason that most cannibalistic snake pictures are of corns. They will eat anything they can get in their mouth unlike BP's.

As for time, it doesn't take long if they are ready. Pop them together for a few hours and see what you've got. If the male is interested, he'll move quickly. I will pair until I know for sure she's gravid and with my original pair, my male has been in with her more than once when she's laid as she never really showed much (even when laying 18-24 eggs at a shot). They don't ovy the way that BP's do so you don't have that to go on. Mainly, I go by behavior. The second she skips a meal, I put the laying tub in with her. It's the only time she'll skip and within a week, I have eggs. Just be sure to watch for a possible double clutch as they sometimes will do. You'll see her looking for a good laying spot and possibly skipping a meal. It doesn't take a second breeding to cause this as they can retain sperm the same way other snakes do.

You also mentioned brumating. Just a heads up, that's not needed to induce corns to breed. I've never brumated any of my snakes and have had clutches (mostly doubles) since 2004 or so. I always have natural light cycles though so that may be what's triggering it. I prefer to feed consistently instead of letting them lose weight during brumation.

Corns are pretty simple and easy to breed. Incubation is also pretty simple. I incubate on the highest shelf on my rack, mark the calendar once they're laid, and watch for pips. It's just that simple. Hardest part is having tubs for all the babies. Good luck and enjoy!