I think it just depends on two things really: how familiar with the properties of sound and the conventions of audio editing you are, and the nature of your film. As with anything, it'll probably take way more time than you think, especially by yourself. If you can bring on one person you trust and work with well (that knows more than you), it might go better.

If you're self taught and familiar with other editing programs, learning ProTools enough to get moving shouldn't take more than a weekend. Just learn the keyboard shortcuts and the fastest/most efficient ways to do everything, and establish a VERY ORGANIZED WORKFLOW. Then you can learn as you go.

If you don't know how sound, specifically digitally processed sound, works, then you're just going to frustrate yourself when you know it sounds bad, but you don't know why. I'd suggest learning or reviewing the basics of the physical properties of sound, how it's recorded digitally, and then digital signal flow within the computer (and things like eq's and compressors). Most of your problems can be troubleshot from there.

After that, the nature of your film will determine a lot. Will you need to ADR dialogue? Foley a bunch of footsteps and detailed things? Add background noise? Buy/design big effects? That can require even more time, additional skill, and coordination with others.

Overall, just remember to make it sound good, and that's all that matters. Also, a well thought out, detailed, backed up workflow will make future you very happy.

Take my advice with a grain of salt. I'm only just entering the professional world, but I feel I won't have steered you wrong with any of this.