Quote from ssmegner:
My experience has been that even on American options they still look at the whole position. If you are assigned then margin comes into play. If you don't have enough in your account the account becomes "Subject to Liquidation". They will step in if they need to but not immediately. In fact they try to phone you up first rather than having some default 24 hour rule. I have been in an insufficient margin situation at TOS for several weeks and they did nothing. The amount was small. Before I dropped Fud-delity they liquidated a position less than 24 hours and for only $5.00 deficiency.
This whole IB vs TOS is not an idealogy war. For me, and at the time, IB cramped my style with what I was doing with options.