POP - I went to two different sub doctors. One was halfway competent and we did the induction at his office. It involved me staying at his office for a few hours and taking increasing doses of the subs until the withdrawal subsided or the max dose was reached. The other doctor was less competent and just sent me home with the bottle. I got precipitated withdrawal with the take home do-it-yourself induction. So, to answer that part of your question - yes, there are sub doctors that do the induction at their office and monitor you in case you go into precipitated withdrawal. The doctor that did it in his office asked me specific questions regarding my withdrawal symptoms to reduce the risk that I was taking it too soon.
When I did the induction at the office I don't remember exactly how long it was since the last dose, but it was significantly less than 24 hours. I was pretty sick (sweating, crawling skin, hot one second and then cold the next). I was not to the point where I was writhing in pain nor did I have digestive 'issues'. It has been a while since then so that is the best of my memory about it. So, in my experience it had to do more with how severe my symptoms were versus how long between doses.
You just need to find an addict with a PHD and then you'll be set!