A while ago I blogged about a timeline of life on Earth extending from its origin in Earth's path to its end in the future (if we don't do something about it). Here it is again.
How long did Mars stay wet? We don't really know precisely but this article at least says that we know there was liquid water 3 billion years ago. So a timeline like this.
To nail down out how hard it is to evolve life really requires looking a bunch of planets that evolved life and a bunch that didn't. Hopefully space exploration will get to there at some point. But until then it sorts of seems that evolving life itself is pretty easy compared to photosynthesis or mitochondria or multiple cells.
Now, you can bring in anthropic reasoning and say that the fact that we're here to observe the result means that we're probably not looking at the typical case and that's fair enough. But there's no reason to think that that luck should have been concentrated at the first stage as opposed to Earth lucking out in how quickly photosynthesis evolved. Or having the many disasters that mostly ended life not having been a bit worse.
And Mars is a lot smaller than Earth is. About 1/3 the surface area. So you'd expect that it would take about 3 times as long for life or photosynthesis or whatever to arise on Mars as on Earth. If we were to assume that everything would take proportionately as long to happen on Mars as on Earth that would mean life but no photosynthesis.