Usually, my female "shows" almost a week before they lay. They're like clockwork now. It's always in the evening about 8:30pm. I always know the day because in the morning when I make my rounds, the two will be inside their "pot" instead of out running around. They must sit in there all day until night time and then lay the eggs. I've been thinking about it and I think I might try to raise this batch artificially. They're due to spawn in about a week now. The female is showing so it looks like another clockwork spawn.
Incidentally, a pair of firemouths in a different tank on the same system are on almost the same breeding frequency. They usually spawn a week after the convicts. I might try to raise them too. All my breeders in this system are still fairly young so they just eat the eggs.