Some lucky people feel better simply from removing the fillings, but most people have to spend months of chelating the mercury out before they will feel improvement (6 months for me) and years before they've completely recovered. Somebody compared it to a leaking boat. Removing the fillings is like plugging the hole, but you still have to remove the water that's leaked in (chelate the mercury).
EDTA is good for lead. It's not so good for mercury. ALA is good for mercury. Occasional use is unlikely to help very much and may make things worse (you may end up redistributing the mercury instead of removing it).
I suggest you do a search for information about the Cutler Protocol if you are using ALA. You can do the protocol with DMSA and ALA, but there are many people out there who use ALA by itself.