Date format in a form in PBCS (Enterprise Performance Management Standard Cloud-Planning)

Summary:

I want to report a timestamp on a form in the format dd/mm/yyyy hh:mm:ss tt by using @calcmgrdatetimetoexcel(@calcmgrgetcurrentdatetime()); and saving the form format from Smartview, but when selecting time format in the member properties it defaults to 0 dp and won't recognise that the time component isn't 00:00:00. I'm guessing that is a 'feature' of PBCS based on the date format in Application settings (set to Automatically detect) as it works in on Prem. Is it possible in PBCS?

My other option is to generate a timestamp via script and upload it as cell text, however as the values will be changing 12 times a day (as well as having cell text members elsewhere throughout the application), the HSP_CELLTEXT VALUE table is likely to get pretty big over time. Does anybody know if there is a limit on the size of this table? Is there a purge that happens behind the scenes to remove any index values that no longer exist in the Essbase data?