Python Flask & HTML - Time in Python

So I am running Python Flask to create a web server which works. I have a text form in the HTML code which gets the user's input. The user has to enter a time, for instance 8:00 or 15:00. It is like an alarm clock, so I need to have a statement in python that says something like "If the currenttime ==(equal to) UserInput: (execute this...)". The problem is I can't have a time in Python which updates every second because whilst that loop is occurring, the rest of the web page cant do anything making all buttons and data unusable. So how would I go about doing this? Thank you