You won't have much time. You'll need to re-clear security initially. T3 has 3 concourses (mini-terminals), so it there's a good chance that you'll need to switch concourses (Concourse A requires getting a shuttle train to/from B & C).
There are 3 F lounges - one in each Concourse. A is the newest and probably best, followed by B and then C (which is the oldest). If your flight is from A, you'll be able to board directly from the lounge. In B - some of the gates are boarded from the lounge, for others, you'll need to exit the lounge and go downstairs to the main departures area.