The GTX 1070 is still a pretty solid card for 1080p, but I get that with high graphics settings and stable fps it's getting tight for you now. If you're mainly playing at 1440p or higher then yeah, it's definitely time to think about an upgrade.
As for timing... it depends on how long you can realistically wait. Usually new generations come out on a regular schedule, but it's not like things change that much if you wait a few more months. That said, if you're willing to spend now, current GPUs like the RTX 4070 Super or 4080 Super would give you a huge boost compared to that 1070. If you have patience and a limited budget though, it's worth waiting because current card prices usually drop when new models come out. In 2026 the market is getting more competitive so you tend to get rewarded if you wait a bit.
What I'd suggest is looking at the rest of your setup: processor, power supply, RAM - are they up to date? Because if your graphics card is old, other components probably could use a refresh too. Maybe it doesn't make sense to throw 600-700€ at a GPU if the rest of the system is a bottleneck. Take a look at what you mainly use for gaming and let me know the rest of your config, that way it's easier to figure out if it's worth waiting or not.