Super-duper technically, if you were really babysitting a terraforming project, you could optimise the time taken by not leaving the auto order interrupt to tell you a dangerous gas is gone, but wait until it goes below the danger %age, then switch orders to do something else. For most dangerous gasses, it'll only save you pretty small amounts of time though, unless you were terraforming a pretty big planet with not very many minimum tech terraformers, and you happened to have a couple of them being GHGs, on a world that needed warming (but not too much), so you could also add less SGG. Then you might actually save a couple of years. That is a preeeeetty rare case though, and a lot of micro for probably not much return
>> I have occasionally seen this for CO2, which I think has a higher threshold to be considered dangerous, but no other gases
Yes, 5000ppm, as opposed to 5ppm or 1ppm for a lot of the other dangerous gasses. For the 1ppm ones, you'd have to be advancing time at one construction cycle at a time