you don't need a microcontroller to make a working timer with enough power to control a contactor. A simple 555 IC can make a timed latch with only a 5V linear power supply (or an old phone charger 5V smps), capacitors, resistors, a DIP Switch, an NPN transistor, and an optotriac-triac stage or a relay.

the idea is to use the DIP Switch as a resistor selector, so the on time can be selected through a variety of resistors that; using the 555 monostable formula represents the time in a single unit

why not a potentiometer?

because, even when a potentiometer is more precise than a chain of resistors you still need to mark the positions for specific time units (1, 2, 3, 5, and so)

the capacitor can be used to set the multiplier for the resistor time units, using a SP2T switch you can select a 1x multiplier and a 10x multiplier, meaning that you can set from 1 minute to 1 hour