Well the website says 10-30 days between all the sizes but I would personally say that's how long you should wait with the in-between sizes, then when you get to the actual sizes leave 6-8 weeks just to give your ears a break.
I'm not 100% sure though... for me it's going to be trial and error. I'll just do like I did with my other stretches and if it doesn't want to go in, I won't force it. It might take 10 days or it might take 10 weeks, I'm just not sure yet.
I have 1/2" lobes and 11 piercings: left helix x2, both conches, both nostrils, septum, navel, and VCH.
My lobes are small but I know a lot about stretching and how to do it safely, so message me if you have any questions!