I am working with RCT data in which patients followed-up at the following time points: 2 weeks, 6 weeks, 12 weeks, 26 weeks, and 52 weeks.

The generic way that I have been attempting to set the data as panel data has been with this command:

Code:
mi xtset participant_id time
       panel variable:  participant_id (strongly balanced)
        time variable:  time, 0 to 52, but with gaps
                delta:  1 unit
However, this does not solve my issue as the delta is obviously not changing by 1 unit, but by the units mentioned above. I have read through the help files and done some reading online, but I cannot find (or at least am not understanding) anything on how to vary the time variable between observations. Any help would be greatly appreciated.