How Long Should I Charge My Garmin Zumo XT

As some here may recall, I have been using my Garmin Zumo XT on my e-bike. Now that I am using the vehicle power cable and a 12 volt power supply in the house, I am wondering how long I should charge it before use. For example, say I don't use the Zumo XT for a week or so and I am preparing to go on a ride and use the internal battery power, how long does it need to be charged to be fully charged?

https://www.garmin.com/en-US/p/679804/pn/010-02296-00