On edit trigger that inserts timestamp dependant on checkbox value

I'm trying to develop an inventory sheet for my company I work for in Google Sheets. In the system, I'm wanting if a checkbox in Column C is ticked it will display the "checked out time" in Column D, and if unticked will display the "checked in time" in Column E. However, I'm wanting when the item is checked in, the checked out date/ time cell turns back to blank.

I've used this custom function script to create a TIMESTAMP function that works, but every time the spreadsheet is reopened is recalculates all the date to the current date/time. Any way of making it non-volatile?

function timestamp() {
  return Date();
}

Would I need a onedit trigger that could do what I described above?

WARNING: I'm not scripting savvy at all.I've been scouring the forums for the past week and can't get anything that works. Any help would be greatly appreciated :D

Link: https://docs.google.com/spreadsheets/d/1Oj6eustjvk9opXFNR2jHa0uMjPnKVXsvwOxFjb1t7-8/edit?usp=sharing