This came up in conversation recently and I realized I don't actually know the answer. Free rooms on most cam sites let you watch indefinitely — the time limits are usually just for private shows.
Battery drain on mobile during live streams is real. Keep your charger nearby if you're watching for a while. Video call before you meet — it's the fastest way to confirm someone is who they say they are.
Never share your real last name, address, or workplace before meeting someone in person.