You can file an accelerated patent where evaluation of the patent is essentially guaranteed within one year. There are definite positive and negatives of this newer approach. Most IP firms do not use this technique and instead use the traditional process.

If my understanding is correct, the patent office can accept, change, narrow or even deny your claims. With a good firm, you should have feedback throughout the process and know where you are going but essentially you aren't protected until the patent is granted. If another company comes up with infringing technology, and it has also filed similar patent, it can come down to filing dates of provisional patents, completion of reduction to practice, etc. I don't believe you are protected and can claim infringement until your patent issues however...