Calculating time difference: I would like to perform an operation in GuiXT if the user has pushed a button within 20 seconds...
In the GuiXT documentation you show how to calculate the number of days between two dates. Is something like this possible for time variables?

You can calculate the difference on your own as follows:

Set V[hms] &V[today_hms]
Set V[sec] &V[hms](1,2) * 60
Set V[sec] &V[sec] + &V[hms](3,4) 
Set V[sec] &V[sec] * 60
Set V[sec] &V[sec] + &V[hms](5,6) 

if  V[sec_prev]

  Set V[diff]  &V[sec] - &V[sec_prev]

  Message "&V[diff] seconds" -statusline


Set V[sec_prev] &V[sec]


Note: if the date has just changed, the resulting "midnight" case leads to a negative time difference that you may handle separately if necessary.