One month timer circuit
Even the tiny and cheap PIC 10F200 can do this.  It comes with a built-in 4 MHz oscillator, which means 1 MHz instruction clock, which you can divide down in firmware to get any length delay you want.

The easiest on this part is to use the timer wrapping as the base event for your clock.  This is a 8 bit timer, so that would be every 256 instruction cycles, or every 256 &micro;s.  The firmware spins in a loop waiting for the high bit of the timer to change from 1 to 0.  It then runs the code to process one more clock tick, waits for the high bit to become 1, then goes back to the top of the loop.  You can easily do all the clock tick processing in 256 instructions.

You want to delay about 30 day, which is 2.6 Ms.  at 256 &micro;s/tick, you need to wait 10.1 GTicks, or 233.2 ticks.  You therefore need at least a 34 bit counter.  Since it's easier to use whole bytes, use 5 bytes for your counter.

Initialize the counter to the value for 30 days on startup, then decrement it by one every clock tick.  You then check it for being 0, and activate your switch when it is.