I have a file , schedule-like, with one record by every working-day, and a portal related to a tasks file. I know the multiple solutions given for my question (calendars of every kind and complexity that I have tried to adapt) but, finally, this is the most easy solution.

My question is :

Simple answer: Loop. You know how many records should be created, from the overall time interval and the increment interval (or just stop at the last time).

For one day, you create a record starting at a certain time, then create another adding the increment (like 15 min.), then continue until you get enough records for the day (or reach the last time). That's one day. The date would be set into a global first, then set into each record. The time would add the interval to itself.

Try it with a test file. Don't put Allow User Abort [Off] until you've got it right. View as Form speeds up Loops.

Alternatively, you could do the above, but make it a separate "fixed" file (table in 7), with only a global date field. Because the times are fixed, only the date changes. Then set the date, and Import into your schedule file, with Add new records. This might be a tiny bit faster.