What the achievement asks
Complete a hundred construction projects in Mechagon. Ten points, account-wide, both factions.
Construction projects are the island's daily community effort: everyone on the shard contributes materials towards one project, and when it fills, it completes.
One a day, so a hundred days
The projects reset daily. That is the whole shape of this achievement: there is no way to do two in a day, no catch-up mechanic, and no way to speed it up.
A hundred projects is therefore a hundred days of logging in and contributing. It is the longest single grind in Mechagon and one of the longest in Battle for Azeroth.
Start this on the first day you set foot on the island, before anything else. Every other Mechagon achievement can be finished inside the time this one takes, so any day you skip is a day added to the end.
Contribute, do not complete
You do not have to be the one who finishes a project. Contributing to it counts, so a few materials handed in is the same as carrying the whole thing.
That makes the daily cost about a minute once you are on the island, which is why the sensible habit is to hand something in the moment you arrive rather than leaving it until you are done with everything else.
What else the same trip gives you
The island rewards being visited daily anyway. While you are here:
- Junkyard Apprentice wants 250 Junkyard Tinkering crafts.
- Junkyard Architect wants 30 blueprints unlocked.
- Outside Influences wants 15 quests from the visitor of the day, and the visitor changes daily too.
- Rest In Pistons has rares gated on which drill rig is running today.
None of those finishes faster than a hundred days either, so treat the whole island as one daily habit rather than four separate errands.