Can the Bitcoin halving be delayed?

Question

Currently the next halving date is May 2020 (provisional) according to enter link description here.

I understand that every 210k blocks, the block reward is halved and this works out, roughly, to once every 4 years.

I guess I have two questions: 1) The 2012 halving took place approx. 3.8 years after genesis, and the 2016 halving took place a further 3.6 years after that. During this period hash rate increased almost continuously and at exaggerated rates due to continuous developments in mining technology from general to specific solutions (CPU -> GPU / FPGA -> ASIC). So were these 'premature' halvings due to the positive rate of change of hash rate?

2) A halving on 23 May 2020 is roughly 3.9 years from the last halving. It seems this is linked to 2018's drop in hash rate, could a hash rate collapse lead to a delayed halving event (i.e. adding the current 210,000 blocks takes longer than 4 years)?

Thank you.

Answer 1

So were these 'premature' halvings due to the positive rate of change of hash rate?

Bitcoin is designed to keep the block time at 10 minutes. The difficulty increases/decreases as the mining hash rate increases/decreases. At this 10 minute rate the the halving event comes every 4 years. As miners started using ASIC chips to mine blocks, the average time came down and that led to slightly lower halving time.

could a hash rate collapse lead to a delayed halving event (i.e. adding the current 210,000 blocks takes longer than 4 years)?

If hash rate declines continuously so that even after difficulty gets adjusted to account for lower hash rates, miners continue to lower their hash powers, then it could take longer than 4 years.