In the case that you're preapproved I would go for it. My complaint about capital one is they pull all 3 reports but if you're okay with that hit I still think you could very well get approved. Safest bet is 6 months but I like to go with "why not try" if I see a preapproved opportunity.
Depending on which, if any card, is offered to you on the pre-qualification site, you might want to get it now or to wait until at least 6 months have passed. The most recent Cap One card I got was a Quicksilver Visa Signature, and when I checked the prequal site over the last 6 months, all I got offered was a vanilla Platinum. However, on my last visit there the other day, I was once again offered a Quicksilver Visa (with very good BT offer), so you might want to take that into consideration.
I have the CapOne Platinum low limit card, and am pre-approved for a QS cash card. I know that most people say wait 6 months between CLI requests but does that also hold for apping for a second card? I’m in my fourth statement month right now. Should I hold off or is it safe enough to app now? I don’t want to app if they’re going to decline due to my current card being too new.
Don't do it OP! Cap One limits you to a new card/CLI every 6 months. You'll waste a triple pull.
Read up here and look around at other cards. During my rebuild - I first went with Cap One, then PC'd my Platnium to QS and app'd Disco.
I doubt they will pull if he is not at 6 months.
However, I have not heard of many being prequal then denied.
OP - just wait a few months, maybe your APR will go down also.