One thing i have seen spending time with an Aerobatic flying school, that hours in the air account for zip most of the time... we have seen 10,000 Hour airline pilots fail to recognise stalls, and really struggle to grasp advanced manoeuvres, yet low time PPL's pick it up real quick and can win aerobatic competitions with only a few hundred hours. or in some cases, before they even finish their PPL.
even the worlds highest time B747 captain admits himself, from his book, he doesnt have 30,000Hours flying experience, he has the same hour, 30,000 times.
Its the High time pilots that come in looking to do an aerobatic endorsement, bragging that this will be easy as they have so many 1000 hours in whatever, are the ones who make the biggest mistakes.
as for the question, When is a stall more likely to happen? the correct answer should be.... "when i make it happen"