May close early. Will almost certainly be scaled back. I would apply for my max allocation if the traded price is well above the SPP price, however beware of selling current stock on-market to fund the SPP purchase because if there's a scale back (as there usually is when an SPP is oversubscribed) then you may not get what you apply and pay for.
I have had a number of cases where I have ended up with a small percentage of what I applied for, and ended up having to buy back more stock on-market at higher prices - so I have learned to do the selling AFTER I receive notification of my allocation - which would be after the SPP has closed - best to actually wait until you see those shares in your CHESS Holdings actually, and then you can reduce exposure, rather than sell first and find out you didn't get allocated what you thought you'd get allocated.
This is general advice based on personal experience only and I have done zero research into this particular SPP, but oversubscribed SPPs get handled in different ways by different Boards / Company Management teams, so I have learned to expect the unexpected with SPPs. Rights Issues are much more straightforward.