Already have the intention, then buy. When to buy, when you have money. Bitcoin is an expensive coin. If you already have the intention but still don't have the money to buy, don't force it. Just wait until your finances are good. One way even though you don't have much money is to buy as much as you can afford but the process must be routine. This is known as the DCA purchase method.
Over a period of one or three years, the purchase process is carried out routinely, so when that period arrives, of course the amount of Bitcoin has accumulated. Estimate for yourself how much with the amount of financial ability. I think so and for me it is so much simpler than having to endure the thought that it is too late to buy.
That is great way to buy Bitcoin. If you want to invest so first of all it is very important to do it when you have enough money and you are financially stable. Bitcoin can be very expensive so it is very important not to buy it if you are not financially ready. Instead of this think about using DCA method so you can reduce risks of market going up and down and risks of buying at wrong time. With doing this you will get more Bitcoin over time and it is less stressful way to invest than worrying about missing your chance.