Hi eileen,
That depends on how good is you Q no. If your Q no is good, do you think those in front of you easily gave up? I certainly think 'no'. But it is possible for those Q no around 1100+ to 1200+ because at that time not much HDB flats (good one) left and even if so, the flats are like 1st,2nd storey and most don't want it already. Then, it can certainly happen.
But, if this scenario did happen at early Q no, the HDB officers have a choice not to call the immediate Q no and wait until the next slot. For example, your is 11AM and you reach early at 9AM, get a Q No and if the 9AM or 10AM slot couple didn't show up, they didn't call the next Q and wait until 11AM, then call. You've no choice but they have la.
I already received the booklet + instructions from HDB and they said that if a couple didn't show up for their slot at their allocated time, they've to wait until 12:00 noon(for those who are late at morning) or 4:00 PM (for those who are late at evening) for their turn.