I just booked my wife booster shots and managed to get early next week by refreshing until someone cancels.
Your refresh the center by switching center. Ie assuming you want sun yat sun, keep switching between jockey club and sun yat sun until a slot pops up. Today while playing with the system at 1050am I got an 11am slot
Anyway, Pfizer kids is now fully booked without April opened. Partly cos currently kids have double booked due to the system 3week gap. I then realise I should not just cancel my booking but pass it to a friend kids by doing what I said above. Ie cancel on one PC and immediately capture on another PC
PS fast fingers are needed