gw does not deamonize itself, but it does sleep and wait for the interval.
You need to nohup it in background to make it immune to hangups etc.
I'm not quite sure what "next Saturday for 24 hours" is supposed to mean,
but "next Saturday" would be
nohup gw -dmy_db -rewalk="saturday" &
If you want daily repititions you could use
nohup gw -dmy_db -rewalk="every 24 hours" &
Or use your system's scheduler with just -rewalk (no timespec). On unix
systems it's called cron ("crontab" command). On NT it's called task
scheduler ("at" command).