Chronomage missions are a great way to get AA, see some old content zones and get some loot for levelling muting. You can also buy a replica of one of the boss mobs of the zone to place in your house. Elquinjena has a fabulous list of all zones, with level of zone and mentor level needed. She has also posted pictures of all the replicas. Many of these zones are now soloable too. The mentor level that Elquinjena suggests will always allow you to complete the mission, however it may make some of the nameds in some zones grey. If you are after the full whack of AA available, I would always check the level of the nameds in the zone on wiki and make your decision on the mentor level from that.
Chronomage mission quest givers can be found in Qeynos Harbour (opposite Antonia statue), East Freeport (through pub), Gorowyn (housing section) and Kelethin (near Grassy Knoll entrance).
Chronomages (for the actual mentoring) and Chronomage merchants can be found next to the mission givers. The exception is Neriak, I have only found a Chronomage (no quest giver, merchant) in the status merchant building at Dockside markets. If there is one – someone please tell me!
The missions are daily and seem to switch at 1am (UK time) each day. There is a time limit of 2 days on the quest.
I have had huge fun going back to some old zones and going into some zones I had never been in 😉 I definitely recommend these for fun.