Often, additional strikes are added to a given expiration as the expiration gets closer to expiring. For example, the Feb AAPL option chain has strikes every $5, but next week's AAPL option chain has strikes every 2.50 for close to ATM strikes. Is there a specific time of the week when the additional strikes get added?
I recall it is added every Thursday for the third week expiration date for the weeklies, read it somewhere on cboe years ago.
I believe it is up to the exchanges, but each can vary and they can change at a whim. Sort of like how many traders blow up because their brokers often randomly change the margin requirements at a whim, and with no warning. I believe at one time Karen (The super-trader) lost a big chunk of investor funds to a surprise like this which liquidated a number of assets. Sometimes the exchanges drop the ball totally, this is part of the reason why things like the Game-Stop squeeze got so bad... there were badly needed strikes that failed to be included on the chain in time; the exchange was too damn slow to add them in which compounded the problems. I felt sorry for the market-makers in that mess.