Help with clock that takes text as input for timer

I'm trying to create an app that puts on a pump; there is a textbox where you type in the minutes (how long you want the pump to be on, then it will automatically turn off.) I have built a board to go with this app on arduino.

My issue is using the clock. I read the clock guide and a comment noting 'the perils of clock' mentioned having issues with an external device, i.e., like Arduino. I'm new to this so I'm not sure how to go around this.

(I realised that text cannot be added, the addition in the button1 click block gives an error.)

Simply, I need help finding out:

  1. how to use the inputted text, convert it to a number, and use it to start an internal timer
  2. what the TimerInterval should be for working with an Arduino


I would consider an alternative approach to pump sleep settings.

Instead of burdening the phone with staying awake long enough for the time to pass, send a message with a sleep setting to the Arduino like S0030 for a command to run the pump 30 minutes then stop.

In the Arduino loop, compare timestamp values to see if there is a passed deadline for turning off the pump and respond appropriately.