When should I build a PC around an RTX 5070 Ti?

If your current PC can take the card, try using it there before committing to a whole new build. Check the power supply's capacity and available power connectors, as well as whether the card physically fits in the case.

It's also worth checking what makes the motherboard incompatible before ruling it out. If the card won't work in the current system, that settles it, but you may not need to replace everything just to get started.

I wouldn't put the build on hold just because Cyber Monday is coming. There may be discounts on individual parts, but a big saving across the whole build isn't guaranteed. If the parts you want fit your budget now, there's a decent case for building now and enjoying the card.

Reuse is worth investigating, especially for storage, but check the details before buying a motherboard. Your three 8 GB RAM sticks need to be compatible with the new board and CPU, and a three-stick setup may not be the ideal memory configuration for the platform you choose.

The three 250 GB drives could still be useful, though you'll want to check their connection types and how many the new board supports. Whether moving them over is worth the hassle depends on how much storage you need.

Nobody can reliably tell you when component prices will be best. Set a budget and price out the complete build, then compare it with any sale prices that appear. If the total is too high, waiting for individual deals is reasonable, just don't assume the holiday sale will fix it.