Runestone Rush

They seem to be on a rotation.
Runestone locations:

/way 47.36 58.64 Elrendar River Runestone
/way 39.13 56.85 Ath'ran Runestone
/way 61.76 61.72 Dawnstar Spire Runestone
/way 41.15 73.81 Sanctum of the Moon Runestone
/way 40.46 13.59 Sunstrider Isle Runestone

Some of these are a little unclear on what to do.

You basically see a runestone icon on your world map, they rotate in order, one is always up.

Once you get to a runestone you turn in Latent Arcana until the progress bar reaches 100%.

Once the runestone is at 100%, you just kill monsters or interact with the objects in the zone until a named boss spawns.

They're supposed to have an objective bar that fills up to 100% but some of them are bugged and might not show.

My observations are that the runestones indeed go in a rotation. After one is defended, the next one becomes active.

The order I saw so far (not confirmed by watching multiple days yet)
/way #2395 41.15 73.81 Sanctum of the Moon Runestone
/way #2395 40.46 13.59 Sunstrider Isle Runestone
/way #2395 47.36 58.64 Elrendar River Runestone
/way #2395 38.33 55.53 Ath'ran Runestone
/way #2395 61.76 61.72 Dawnstar Spire Runestone

Easiest way to do them all in one day is by dropping the quest and picking it back up (only to have a visual aid on, like @Maraxus said it also works without dropping)