If the earbuds go into standby mode and turn off, you can still use them without putting them back into the charging case. 
You can reactivate the headphones by pressing or touching the outside earbud itself.
Please note: They will be automatically powered off after 30 minutes of being in standby mode if they disconnect from Bluetooth. To reconnect, you will need to put the earbuds back in the charging case and take them off again. 

It is possible to change the standby mode time with your headphones. To do this, go into the My JBL Headphones app and choose the Standby Time via Auto-off function. You can adjust the time to 15min, 1hr, etc., or you can choose “Never” if you want to keep the earbuds turn on at all times. Once you set the Auto-off, the earbuds will work according to the setting whether they connect to Bluetooth or disconnect.