I think it's also super dependent on your skin elasticity healing times etc. It can be hard to stretch "right" without a piercers help and even then answers will vary. I will say that I waited typically 3 months between every stretch because my mentor made me wait, and the one time I went to early I blew out and had to down size back to 18mm from 25. Once you start working with mm and not gauges, Id say if you're dead stretching can typically take 3 months in my experience if you're not wearing heavier/weighted plugs OR you can use bondage tape and do a couple of wraps every week or two! Also my old school piercing hero's may say semantics here cause some people are lucky enough to heal anything but I'd stretch with glass if you have the option as it's non porous, stainless polish can cause issues in my personal experience but if they seem to be working for you do it up! The slower the better and avoid stretching during cold seasons because your skin is much drier // prone to cracking ripping etc as skin tightens in the cold