Question about private onsen time length

I’m going to be reserving a private onsen in Hakone for my girlfriend and I, and am unsure how it works with a 2 hour reservation.

The place we are planning on going only allows reservations in 2 hour increments, however I see a lot of people online saying you shouldn’t be in an onsen for more than 10-15 minutes at a time, especially as a first timer?

While I think we will want to be in the water for more than 15 minutes, 2 hours does surely seem like a long time, especially wanting to be able to see other things in Hakone during the day (most attractions seem to close around 4-5 PM).

Is it considered rude to leave the onsen early if you’ve booked a multi hour reservation? If we booked for 2 hours but left after an hour, is that frowned upon?

by bruthamane