In MuHelper you can see a button OFF HELPER
so you can close the client, but your character will still be in the game leveling up!
For non-VIP members limitation of time is 480 mins.
for VIP members there are no limitations of time.
1. Open MuHelper
2. Press "Save Settings"
3. Press "OFF HELPER"
4. Close the window from the "X" in the top right corner