The Apex "If Feed" command has an optional timer parameter where you can tell a device to stay off or on longer than the built-in Feed timer. The Feed A, B, C, D timers are defined under the Misc Setup screen:
In my example, if I click Feed A, the timer will run for 300 seconds (5 minutes). Using the "If Feed" command, I can instruct my return pump to turn off during the Feed A cycle like this:
Set ON If FeedA 000 Then OFF
The 000 parameter is the number of additional minutes beyond the built-in FeedA timer of 5 minutes. So in this example, the return pump will turn off when I click Feed A, and remain off for 5 minutes as the Feed A timer counts down to zero. As soon as the timer expires, the return pump will turn back on.
But If I change that 000 parameter to 005, then the return pump will wait an addition 5 minutes beyond the Feed A countdown timer, so it will remain off for a total of 10 minutes.
So using the example you requested, if your Feed A timer on the Misc Setup screen is set to 300 seconds (5 minutes), you would use this code to turn off your powerheads for 15 minutes and your return pump for 45 minutes:
Set ON If FeedA 010 Then OFF (total of 15 minutes with the 5 minute FeedA timer + 10 minutes extra delay)
Set ON If Feed 040 Then OFF (total of 45 minutes with the 5 minute FeedA timer + 40 minutes extra delay)
See my tutorial on Apex Feed Cycles for more details and example code: