Questions about time_in variable

I was wondering about the code for calculating the time in the pump commands in the t-stat experiment.
The code is as follows:

time_in = - (np.log(lower_thresh[x]/average_OD)*VOLUME)/flow_rate[x]

Where the next line limits/sets the result to max 20.
My question is: The “time_in” that is “seconds”?

Ah, and is there a problem to have it >20 seconds?

There is no issue if the pumps are matched. If influx > efflux flow rate, then media might accumulate in the vial, potentially causing overflow. 20s is an arbitrary value that we’ve used to prevent overflow. You can tune this to what makes the most sense for your setup. Just be careful of any overflows.