Let me give you a client example. I met with a client last week who held a mid curve 1-2-1 Euribor butterfly from April 01, 2016 until July 25, 2016. As I recall, his net on the trade was about +$900. I think his initial spread margin to carry the trade was like $400. His max drawdown might have been a couple hundred bucks. Unless you have some sort of arbitrage worked out, at least in my mind it doesn't make much sense to trade these things in a high frequency day trading fashion. But you can swing trade these things for cheap and build up some equity in your account. And when you get going on it - lever the piss out of them.
Depends on your clearing firm. Mine will typically debit or credit my account to the day's settlement. They charge me $1.00 per R/T in terms of commissions more for "maintenance" on carried positions. Initial margin is the margin that market participants must pay when they initiate their position with their clearing firm whereas maintenance margin is the minimum level at which market participants must keep in their account, or "maintain" in their account over time. http://www.cmegroup.com/trading/int...ctor=INTEREST+RATES&exchange=CME&pageNumber=1