If you would like to stay in the lounge longer that the specified time you are more than welcome to make as many reservations as needed to cover your time in the lounge, but this will need to be with the lounge directly.
For example, if a lounge visit includes 3 hours and you would like to stay for 6 hours from 2PM - 8PM, make sure you head to the front counter to book in your second reservation from 5PM.
There is no guarantee that this further time will be available, noting that the lounge may have capacity constraints at that time.