These hexes are big!

The scale on the map is 10 miles (16km) across a hexagon. This is 86.6 square miles (221.7 km²). For comparison, that's 25% larger than Washington DC.

You say your characters spent 1 day crossing this area on foot. Realistically, they know next to nothing about it. It is entirely possible to run an entire campaign from 1st to 20th level entirely within an area this big.

For a further idea of scale, Chult is bigger than Great Britain and Ireland:

Aproximately 71 million people live here but the area is still over 80% rural or wilderness. The current record for going from one end to the other of Britain on foot is 12 days, 11 hours, 6 minutes and 7 seconds but that was on roads and not through jungle.

These hexes are big!

The scale on the map is 10 miles (16km) across a hexagon. This is 86.6 square miles (221.7 km²). For comparison, that's 25% larger than Washington DC.

You say your characters spent 1 day crossing this area on foot. Realistically, they know next to nothing about it. It is entirely possible to run an entire campaign from 1st to 20th level entirely within an area this big.

For a further idea of scale, Chult is bigger than Great Britain and Ireland:

Aproximately 71 million people live on those two real world land masses but the area is still over 80% rural or wilderness. The current record for going from one end to the other of Britain on foot is 12 days, 11 hours, 6 minutes and 7 seconds but that was on roads and not through jungle.

To answer the headline question:

If you are familiar with an area you don’t need Navigation but your character’s aren’t.