"ALA is quickly converted by the body to DHLA. It is the DHLA that does the chelating and has the half life of 3 hours"
this is certainly not true. Both Lipoic acid and dihydrolipoic acid have the same half-life of about 30 minutes.
And again, you seem to be confused about what half-life means. Andy never said the half-life of ALA or DHLA is three hours. I have no idea where you got that from. If the half-life was truly three hours there would be plenty left in your system nine hours after taking it.
Andy claims that half-life of DMSA is between 35 and 40 minutes, which means it would be out of your system after about four hours. This is patently not true. the half-life of DMSA is in fact between 2.5 and 3.5 hours, which means even after seven or eight hours there is still quite a bit left in your system. which I clearly demonstrated in my post above.