Parsing a dateTime in a datagrid

I am trying to create a timesheet process and I am stuck at a validation process. I am using the formatting function formatDateTime($Path, 'EEE') to get dates the form of 'Mon', 'Tues', etc, and I would then like to check in the datagrid if it is already being used. I'm a bit stumped. I tried to make a count to keep a track of the number of days used, limiting it to a week, but it was clunky and didn't interface very well (couldn't find a way to hide it) so I scrapped it. I could probably use 5 different boolean's that change depending on if the day has been used or not (using microflows it is doable, but seems like a lot of work to check if a day is in the datagrid), but that also seems redundant, if there is something sleeker to use, or function I couldn't find in my searches. Any suggestions are welcome, thanks in advance.
1 answers

It seems to me like your design might be a bit complicated if you are recording all your timesheet activities in a single generic form. It might be easier to have a timesheet detail entity that records hours for an activity for each day of the week. Here are some screen captures from a timesheet application I made which might give you some ideas for an alternative approach:

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All of the cells for each day of the week are editable with on-change actions to update totals, and each row is linked to a cost center/prtoject and activity type. This used a domain model with a week number, a timesheet and a detail recored for each activity row:

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