I think you mean ethylene, not oxalic acid. Oxalic acid actually delays ripening by inhibiting ethylene production.
http://www.ncbi.nlm.nih.gov/pubmed/21506518
http://www.sciencedirect.com/science/article/pii/S0925521407000816
It also delays fruit decay by inhibiting polyphenol oxidase.
Seems to depend a lot on the variety and species. There doesn't seem to be much information out there but the ethylene production levels of jalapeƱos and habaneros have been measured, and jalapeƱos produce very low levels while habaneros produce much more (up to 10x more). That seems to make sense from what I've seen, because chinenses ripen much better off the plant than annums. If you pick a fully green, fully sized jalapeƱo or poblano it's not going to turn red, but if you pick a fully green, fully sized habanero they always seem to ripen completely, whether the color change has started or not. Ethylene production is triggered in fruit from bruising, cutting, or damaging the fruit somehow, so it is probably triggered when a pod is removed from the plant too. It would make sense for pods separated from the plant to try to fully ripen as fast as possible in an attempt to develop viable seed. Even underdeveloped habaneros usually fully ripen from my experience as long as they're kept at room temperature and not in the fridge. Some baccatums too, at least the ones that don't go through multiple color stages. Frutescens seem more like annums when it comes to ripening though not quite as slow.
I like to pick chinenses at about 50% color change then leave them at room temperature (not even in a bag, just setting on the counter) for a couple days until they fully ripen and (hopefully) encourage the plant to set more pods, but that's just personal preference. I don't notice any difference in flavor, and I believe they reach their maximum heat at the beginning or early stages of the color change anyway, so I don't think ripening them on the plant is going to make them any hotter. Annums I let fully ripen on the plant. The superhots all seem to ripen more slowly than other chinenses, especially the tips, so I let them go longer. I don't know why that is, maybe it's the frutescens genes in bhuts/nagas. I don't know if the Trinidad varieties have frutescens genes as well, but they seem to ripen more slowly than most chinenses too. They don't really appear to have frutescens genes based on the leaves and fruit, but I remember someone theorizing that mostly chinenses/part frutescens appeared to be the formula for all superhots, so who knows.
Of course, that all goes out the window a lot of the time. I'll pick fruit later because of laziness or being busy, or get a little aggressive and pick them earlier when I go on a picking spree.
That was a little long-winded and probably more than you cared to read, but anyway, you can definitely pick most chinenses and some baccatums before or at the beginning of the final color change and have them reach their final color. Annums, frutescens, and superhots you can probably get to fully ripen off the plant if they're something like 75-80% to their final color. Whether or not picking them a little earlier and finishing them off the plant affects flavor is up to you to decide...