You would need your head examined if you were to bid at a property auction on the expectation of a draw down on funds with the way banks operate these days.
Pure madness, as there is a very very strong chance you will be frustrated in some way or other by lack of common sense, and you will loose your deposit.
So in that case, there is an element of a gamble here, and you have to be prepared take a hit.
I had a really good, switched on mortgage adviser, who, even though couldn't foresee any issues that may arise, knew well enough to say, someone, somewhere in the chain could cause a delay which, even though they would be aware of the time constraints, ment very little.
If you proceed, and are successful, you will be extremely lucky imo.