What will happen if that guy got all 5 lots allocated but he can only pay for one lot?
Normally the brokerage/bank gets allocated a certain amt out of the total issue. This amt is then distributed to their clients, ie say their clients bid for $50mil in total and the brokerage only gets $3mil allocation, brokerage will split the $3mil amongst the clients who had placed their bids in a manner that they deemed fit. If one particular client doesn't want to take up his allocation in full, the broker can help to ask if other clients want to take that up.
However, it is very unlikely that a client gets full allocation unless the issue is undersubscribed.
It is also very true that you are invited in the morning and have to indicate your bid by afternoon.

