Why did Thanos not seek the Timestone first, to save his own planet?

Why go to the trouble of collecting all the stones, when simply spending the resources to get the time stone could have been much more simpler.

In short, Thanos isn't looking to "save" just his home planet anymore, but instead, the entire universe.

Thanos considers himself to be a survivor of his home world's poverty/starvation/etc.. And not only that, but he also believes that acquiring all of the infinity stones is his destiny (as mentioned on Vormir). With this kind of mentality, Thanos isn't looking to recover the past, but instead, create a new future.

And then, if you've seen Dr. Strange, then you'd perhaps remember that using the time stone excessively is said to run a high risk of causing major tears/damages in the time-space continuum, would could cause the entire universe to cease existing. Although Dr. Strange was able to perform this act over the majority of Hong Kong, rewinding several minutes, IMO, it would be a much different feat to perform this on an entire planet, and over the course of who knows how many decades/centuries/millennia.

(If someone knows this time difference, please suggest an edit).

I'm not saying it's impossible for Thanos to rewind the state of Titan all the way back to when it was in good condition, but, perhaps it's just easier to create a new one.

Charles' answer is correct, that Thanos wanted to "save" the entire universe, not just his planet.

But even if he would have been happy with just saving his planet, it's unlikely that the Time Stone would have been enough to allow him to do so. Remember that Titan wasn't destroyed by some cataclysm or sudden cosmic force or single thing that he just needed to prevent. It died when the planet could no longer sustain its population. If he went back to when it was already overpopulated, what would he do next? Again suggest that they kill half the population? It would still be rejected.

About the only thing he could do, would be to go back to before it was overpopulated, and convince the entire planet to stop or slow down (depending on how far back he goes) their rate of reproducing. Somehow I don't see that being a very successful recommendation...

At the time of Marvel's: The Avengers, based on what we know by the time of Infinity War, /both/ the Time Stone (Eye of Agamotto) and the Space Stone (the Tesseract) are on Earth. Thanos didn't know whether /both/ were wielded by the same person, or allied entities, which could result in him failing in his mission entirely before he had any Stones at all.

As things went, Thanos acquired the Mind Stone, and sent Loki to Earth with it. Loki encountered the Space Stone first, and the Time Stone wasn't involved. But he still lost.