Is there anything in the script which could cause it to not run its full course please?

[David Raymond]

Not necessarily the cause of your problem, but if you're going to compare dates it should be as objects, or as text as year-month-day. Here you're comparing dates as text in day-month-year format. So January first 9999 comes before May 4th 2020

"01-01-9999" < "04-05-2020"

...
04-05-2020 09:30:00 40
04-05-2020 12:30:00 40
04-05-2020 15:30:00 40
04-05-2020 22:30:00 40
...
input_date,input_time,input_duration=date_time_duration.split(' ')
current_datetime = datetime.datetime.now()
current_date = current_datetime.strftime('%d-%m-%Y')
if(input_date>=current_date):
   while(True):
...