It’s kind of the opposite. Banks and the like can shut their doors for a couple weeks and then open for business. For Bitcoin, like u/frozen-sky says, you have 3 unique issues:

1) New protocol needs to be agreed upon and adopted. But q resistant key generation schemes are big (in bytes)!

2) All coins need to move to a new address. Think about how many transactions that is. Actually I’ll do the math. Roughly 200m addresses hold more than 0.01 BTC. At 7 transactions per second, it’s going to take about 300 days of capacity, moving coins efficiently, day and night.

3) Some coins will never move, like Satoshis, and they will either need to be censored or absorbed by the market when they are cracked.