Storing data through power-outage/reset is not trivial. Probably the easiest solution for single value is to use EEPROM to store the data. There are several eeprom libraries Libraries — XOD
‘buffer’ node is the easiest solution to remember the value & have button-press UPD the buffer node.
I assume “time set value” is about the same as set temperature; use ‘buffer’ to remember setting. The easiest way to trigger an action at some future time is to use ‘delay’ to wait that long and trigger action with DONE pin.