The description of the aarakocra includes a section called Sky Wardens containing interesting sentences such as:
They can spend hours in the air, and some go as long as days, locking their wings in place and letting the thermals hold them aloft.
In general, this section implies that an aarakocra is potentially able to fly for days on end given the right environmental conditions. This is an interesting trait, and a plausible one, as there are indeed real-life birds who spend almost their entire lives airborne.
However, looking at the racial traits, it's not obvious how an aarakocra player character could accomplish such feats. For one thing, it seems that an aarakocra player would still need to land for 8 hours each day in order to take a long rest. That by itself is not terrible, since they could opt to skip a long rest and risk exhaustion from sleep deprivation in order to keep flying, at least for a few days. Probably the bigger hurdle is the forced march rules:
Forced March. The Travel Pace table assumes that characters travel for 8 hours in day. They can push on beyond that limit, at the risk of exhaustion.
For each additional hour of travel beyond 8 hours, the characters cover the distance shown in the Hour column for their pace, and each character must make a Constitution saving throw at the end of the hour. The DC is 10 + 1 for each hour past 8 hours. On a failed saving throw, a character suffers one level of exhaustion.
So it seems that an aaracokra that attempts to remain in flight for even 24 consecutive hours will face 16 Constitution saving throws with DCs ramping up from 11 to 26, and failing too many of these saving throws will exhaust them to the point that they fall out of the sky.
So, am I missing some mechanic or aspect of the aarakocra's racial traits that allows them to remain in flight for extended periods of time, or do the mechanics of the race simply not live up to the description?
Best Answer
The text you cited is the ammunition you need to make the case to the DM, which is where you need to go to get your ruling.
When it comes to flavour and thematic elements of a character, 5e was created around the idea of rulings over rules. It doesn't give a hard mechanic like spellcasting for a feature like this, but instead relies on the player to interact with the DM in rationalizing and making use of this feature if it's present in the lore on the world you are playing in.
If the DM agrees and approves, you're fine with using the feature as described. If not, you'll have to come to an understanding and agreement on expectations, typically in a session zero.
I don't particularly like, "Ask the DM," answers, however this is not a mechanical feature but a thematic one. Those are always ask the DM to see if it fits the DM's world.
As far as Forced March, letting the thermal currents carry you isn't a forced march. It's like sleeping in a raft, letting your wings be held up by the air, just like the raft is held up by the water. There's no work being done by you because you aren't exerting any effort, so there's no need to make Constitution checks, in my opinion.