The momentum to start Bitcoin investment will come when you are ready. If you have much knowledge about Bitcoin investment, you will know when you can start and not just follow others suggestion.
How can you have much knowledge on bitcoin investment and how to hodli for long term if it's not by practicals which is buying immediately you have the basic knowledge and discretionary income. You don't need a special time to get started which is why the DCA method is emphasize for new investors to get started with and continue buying every week or month overtime for 4-10 years and above. You can learn the rest when you have started.
Investing in bitcoin is not by theory because theory wouldn't control your emotions when the market dips and moreover, you don't have any bitcoin so it's easy said than done. Waiting for the right time to get started and trying to have much knowledge on bitcoin before getting started are all waste of time because bitcoin price and time waits for no man. The earlier, the better for you. A new investor is only to be buying and building his bitcoin portion and keep his accumulation journey ongoing till he reaches his bitcoin target.