If you bought in 1929 just before the downturn you had to HODL for 30 years until the price was back where you bought it
But you're missing one major point. And it's that these are crypto currencies and have nothing to do with those events.
BTC is about 7 years old and during these 7 years the price of 1 bitcoin made it from $0.01 to $8200.
Hodling in the crypto world especially when referring to bitcoins nowadays (due to the crazy price fluctuation that has been going on for the past few weeks) is of way shorter terms.
In fact, if you had bought in the beginning of October, you could have doubled your money. Was that 30 years ? That was 30 days

This doesn't guarantee that prices follow constant patterns in any way. Crypto is unpredictable and has a lot of factors that affect it.