[gentoo-user] Using date/time variables in cronjobs?

[Tanstaafl]

Ok, another little thing...

Is there a simple way to use date/time variables in cronjobs? Or do I 
need to use a bash script for this? I prefer simple, and just using the 
variables directly in the cron command would be easier if it works, so 
figured I'd ask first...

I'm trying to schedule a dump of my databases like so:

pg_dumpall --username=username -o -f 
/home/user/mypg_backups/hourly/\%y/\%m/\%d/\%t.sql.gz

But trying to run this command fails with:

pg_dumpall: could not open the output file 
"/home/user/mypg_backups/hourly/%y/%m/%d/%t.sql.gz": No such file or 
directory

Tried escaping the variables and not, same error...