Timer in minutes - howto

hi,
I'm creating a timer dashboard for my hot water tank. I'd like to specify time in hh:mm:ss instead of seconds and set delay based on that. I've added a datetime type variable but I can't set delay for that. so my question: I want give a variable a value of 00:30:00 on a dashboard and delay based on that. can you pls help me how to do this ? Assume its something pin easy, I just can't figure .
another question: is there a way to add days somehow to a dashboard as checkboxes?

I mean I'm looking for creating something like

S x M x T x W - T - F - S 10:00:00 - 11:00:00

to turn something on and off on S/M/T between 10:00-11:00 how to do this nicely ?

finally ditched the countdown idea and solved it with wait for. not so eegant but works.