I'd pick up the breeding trap right away and have it on hand. Last week I had one of my platys giving birth in my 20 gallon. There are lots of floating plants in the tank so I thought some would survive. Alas, they were all stalked and eaten by other platys. No survivors. I picked up the breeder and have it on hand now. Your guppy will be very fat and look like she is about to burst. Don't put her in there until you think she can't get bigger. It stresses the mom out to be in the breeder. My plan is to keep checking daily and try to catch them in the act of birthing-then place her in the breeder. Once she is done having them-put her back with the rest of her tank mates.