At what point has be broken his promise?

If you borrow 1 BTC from me without agreeing any terms of repayment are you a scammer IMMEDIATELY (as you haven't repaid it?) How about in a week's time?  Or a month?  A year?

An IOU can NOT be defaulted on (other than by the issuer stating that they default) unless a means/time-scale for settlement was agreed.

If you disgaree then answer this simple question:  if you receive 1 TF BTC on ripple at what date/time has be defaulted if he hasn't yet redeemed it?

If your claim is that ALL ripple BTC debts should be IMMEDIATELY redeemable for actual BTC then that has some very nasty logistical issues - not least of which being that if you borrow on ripple (i.e. issue an IOU in return for real BTC) you can't actually spend those BTC without being immediately a scammer as you can no longer redeem them on request.  If, on the other hand, your claim is NOT that all IOUs should be immediately redeemable on request then we're back to asking how/when is the agreed redemption of these TF IOUs?

That's ONE of the flaws this little experiment has addressed - that IOUs with no terms are inherently worthless as they can only ever be redeemed if the issuer of the IOUs voluntarily chooses to do so (there's no clearly defined point at which a 'default' can be declared).  Another flaw shown here (which I pointed out and asked about ages back - but it got ignored despite Ripple team answering easy questions in same thread) is that all IOUs are treated equally - just because I issue trust to A and B does NOT mean I value IOUs from them equally or am fine with IOUs from one being swapped to IOUs from the other without any input from myself.