The switch SW1 can be thrown on the other side at starting to get a 30 minute ON delay. The capacitor C2 can be changed to get various timings. The required load can be connected in place of LED D1.

Use the potentiometer for setting the timing period within these intervals. For the 0.3 second to 10 minutes timer version the potentiometer is 100kΩ, R1 = 9.1kΩ, R2 = 910kΩ, R3 = 220kkΩ and C1 = ...