I want to create a circuit that when a button is pushed, one piston goes after a delay from another piston, but when the button is reset (i.e. when it is released), then the same piston retracts first and then the second piston retracts later.
If I understand you right, you want an "ABBA circuit": When you turn the input on, first A turns on and then B, when you turn the input off, first B turns off and then A.
The Minecraft wiki lists multiple designs for those here: https://minecraft.gamepedia.com/Mechanics/Redstone/Miscellaneous_circuits#ABBA_circuit (archive)
More can be found online.
An easy example is this one, using the locking feature of repeaters: