The counters have been wired in count-down mode as only then the counter IC completes its count cycle in a number of clock cycles equal to the number set by thumbwheel switches.
The time can be set in steps of one minute. If the clock period is changed to, say, 2 minutes, time resolution becomes 2 minutes, whereas the maximum settable time delay increases from 99 to 198 minutes. In essence, the maximum time delay that is achievable with this circuit is 99 clock cycles with a time resolution equal to the duration of one clock cycle.
What is vr1 in the above electronic reminder circuit