man autofs
-t, --timeout
Set the global minimum timeout, in seconds, until directories are unmounted. The default is 10 minutes. Setting the timeout to zero disables umounts completely.
If you don't want to set a global timeout you can specify a different timeout for each mount
man auto.master
-t, --timeout
Set the expire timeout for map entries. This option can be used to override the global default given
either on the command line or in the configuration.