I think I would do this with a custom form.
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Use an entry to fill the “first week” column.
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Create 3 math columns called “2nd week”, “3rd week”, “4th week”.
2nd week formula: “First week” + 7
3rd week formula: “First week” + 14
4th week formula: “First week” + 21
- Add a switch pointing to a boolean column to store the “Repeat event for 4 weeks” value.
Then on the Submit button, have 2 branches.
If “Repeat event for 4 weeks” is checked > Use 4 add row actions to iteratively add 4 rows with the corresponding “First week”, “Second week” and so on.
If the column above is not checked > Just add 1 row with the “First week” value.