We are not all aware of the exact price to buy bitcoins so we should set a fixed price and then buy accordingly and hold the investment for a long time as you have implied. Investing in Bitcoin requires us to commit to holding it for a long period of time because if we can hold this investment properly for a long period of time then we will be able to achieve the desired results. Also you mentioned risk we all have to accept that all investments involve risk. But while all investments involve risk, investing in Bitcoin is much less risky.
Yeah there's no best time to buy bitcoin, instead of trying to time the market is better to just focused on using DCA strategy to accumulate Bitcoin, by buying at different price interval with a fixed amount of money either monthly or weekly. Dca is one of the best method in accumulating Bitcoin and it has helped alot of investors gathered some good stash of Bitcoin in their portfolio, and it has also save us the stress of trying to time the Market .
You are right, it will be very difficult to be able to invest using this method if we don't have a steady income because it could be that when we have a purchasing schedule that we have set and we don't have the funds, of course we won't be able to buy according to the schedule that we have set. However, it would be better for us to buy according to our abilities and not force ourselves to buy if we are not yet able to invest
When it comes to DCA one don't have to go all in at once to start his accummulation, one can start by sharing his earning with percentage , like using a certain percentage for investing ( accumulating bitcoin) and holding the remaining percentage as fiat (emergency funds) to coverup any expenses while they invest in Bitcoin. So one can even start with the amount as low as $10 to run DCA of weekly purchasing. That why is better to spend long time in your accummulation processes , while holding because as time goes on you will see yah portfolio growing with time and as you continue to hold as the value keep increasing you will surely endup with some delightful profits due to the quantities of yah holdings.