Ooooh ok so employees earn time off when working overtime in essense. They can then use this time once it is approved. This is what you would like to track. This is def doable and I have done similar things in the past. Here is the layout/screens I used and we can go from there.
Home Screen - this screen just tells the user who is logged in and also lets them choose from an array of buttons that take them to other places in the app.
User Profile - this screen shows the user totals such as hours worked etc and in your case will be their HUB for how much time off they have. Generally I also display a gallery that holds the user's past/current time entries but in your case it would be past/current time off requests and their dates and status.
Admin Screen - this screen will only be accessable for certain users such as yourself. This is where you will be able to do admin type functions such as add time off to someone profile or accept a time off request etc. This is also generally where I put any buttons for admins to run Power Automate flows to generate any reports they may want etc.
User Submit Request - this screen will be where your end users are able to submit a time off request from the app. This will allow them to select dates/times, number of hours, and whatever else you want to or need to track.
This is a good starting point for an app like you are talking about. I will show you some images of the last one I did that was time tracking. This app is used to track how many hours are worked per day and how many of those hours were for each project as projects are billed for their hours.
Home Page:
User Profile:
Clock In/Out:
Hope this helps or at least gets the cogs turning for you! =^D
