If the policy includes Maintenance > Update Inventory as part of a Self Service policy, then JAMF has purposely included a delay of a number of minutes. The logic being that if a user was to click on several Self Service policies and one or more included an Inventory Update, it would add a lot of time and successive "recons".
You might consider creating a script that issues the command to do a recon and then restart that will run at the end of the Self Service policy.
Just warn the users that it will reboot and it might occur before any other Self Service installs take place.
