You can go for months or even years with no loss of the GTMHP data and settings that you have saved. However, Local Storage is subject to loss by such actions as you yourself clearing cache memory. You should periodically backup your GTMHP content.
There are many ways to save/restore your data. One method is to Copy your data and Paste it into a text editor to be saved as you would save any file, including to whatever Cloud services you might use. That file may later be restored by pasting into the window shown during the GTMP Restore process.
A direct method is available to GTMHP Account subscribers which allows direct save and restore of your data at the GTMHP Internet site.
Besides a backup, the Save/Restore process allows you to access and update your GTMPH settings and data across all your devices.