You can take the ALA for about 3 days on, 3 days off if you wish, or extend it further. Whatever suits you. Most people just do the 3 days on routine and 3 days (or more) as a break.

You should not miss a dose. The whole point of this 3 hourly routine is to keep the chelating agent at continuous even levels in your blood. if you miss a dose, the levels of ALA will drop sharply in your blood stream, then when you take a later dose, they will spike up again and this is what makes the movement of mercury unpredictable and thus risks it going into more sensitive areas, which can make a person suffer the backfire effect (redistribution).

You can of course extend it to every 4 hours during the night and then go back to every 3 hours during the day (to help you get a bit more uninterrupted sleep). If you miss a dose(by accident) you should not continue the round, but you should instead stop and wait for a few days and start again. Being a bit late in taking a dose maybe acceptable if it's not "too late".

Some people can chelate for a whole 2 weeks non stop, but most do not like to do it that way, unless chelation happens to make them feel better on round. However, it's not such a good thing due to the interrupted sleep patterns and of course the need to rest and give the body a break between rounds. ALA apparently also increases the uptake of copper I believe, and I think "zinc"? (Not sure on that one), which is why it's not good to be taking it for "too" long in one whole stretch. 3 days or so is pretty adequate for a round.

You may also need to watch any supplement intake that contains copper (and zinc? not sure on the zinc). whilst using ALA. Also yeast levels can flare up too with the use of alpha lipoic acid, so that may also need to be addressed. DMSA can do that as well apparently, but I notice ALA is more problematic in that area (for me).