1. see below
2. yes
3. see below
1&3 are highly personal and subjective to each individual and his or her own circumstances. Cuivre has it right: your time to withdrawal will depend on not only what opiates you've used, but also how long you've used/abused them, how often you tend to dose (how long your body is used to waiting will change the outcome), and your physical metabolism. But it also depends on a lot of other factors: your emotional/mental situation, your metabolism and physical fitness level, what you're eating, whether you're in a different environment than the one in which you're used to using/being. This is just something everybody has to figure out for him/herself. Very generally, it can take anywhere from a few hours to a few days. Some people (especially first time users/abusers) can abuse opiates for several months without getting any withdrawal symptoms at all. Some people get symptoms after as few as a couple of weeks.
1/3. 3 is also a very personal question as everyone's addiction works differently and has different triggers, strengths, and resource potential (for both continued abuse and recovery). Some people prefer to go cold turkey. I'm of this ilk because when it comes to opiates, the self-control and patience that is so present in every other aspect of my life just flies out the window. If I'm tapering, or maintaining, I have to be held accountable by an outside party. This is just the nature of my addiction and I've learned to work within its confines. Tapering, however, is less acutely uncomfortable and can be more successful depending on you and your set of resources. Either way, the chance of success without a plan in place for after the withdrawal and for continued recovery is very, very low. Quitting the drug is about 20% of quitting the drug, if you catch my drift.
back to 1: I've found that, since about 80% of withdrawal is mental, if I put myself in a totally separate location/environment/circumstance than I am in when I'm using, the withdrawals are FAR less uncomfortable if noticeable at all. This is my biggest suggestion to people, followed by making sure your support system is set up and not quitting until YOU, personally, WANT to quit. That desire can't be for anyone else, or from anyone else, or it won't work.
Good luck.