This is a SCR timer circuit. Here, SCR is used to drive the final actuator, the buzzer.  The time constanst of this circuit is determined by  R1 and C1. The buzzer will sound when C1 charges up to a desired level, it will cause the Q1 to conduct and triggers SCR1.  The use of FET for Q1 make the RC constant can be very high for very long time delay, make this circuit has very wide  range time setting.  Here is the schematic diagram of the circuit:

Scr Timer circuit schematic