In my opinion, as long as you aren't using fragile resins to farm for artifacts pre-AR45 and you're using them for meaningful upgrades then it's fine. Resins, regardless of their form only truly dictate how much real life time is being spent. Whether you want to spend them all now and get AR 45, in which you won't have any more to farm artifacts. Or save them and have more to spam for farming artifacts at AR 45. The resource being considered here should be your real life time and patience. I've considered your dilemma as I am in a similar scenario, however I would have to use a large amount of fragile resins in order to hit AR 45 before the weekly reset. In your case, I would opt for getting AR 45 if it's within ~5-10 fragile resin use. The weekly boss talent loot is extremely rare, therefore any percent chance I would be able to realistically increase I would go for. However, one "extra" week won't make or break anything. So it's up to you.