Actually, the use of "" or {} does not matter in this case, as there is nothing to be substituted in the preprocessing phase.
What is to be kept in mind, however, is that the mask is matched against "minute hour day month year" every minute. If the mask matches, the associated command is evaluated. In your case, it means the command will be triggered once every hour, twenty minutes to the hour (01:40, 02:40, 03:40 ... 23:40).
To trigger something every 40 minutes, your best option is most likely to use a recursive 40min timer.. Most basic version is shown below:
Code: Select all
proc someproc {} {
...
#Now a recursive call
timer 40 [list someproc]
}