In order to decide when is the right time, you have to know all your options, and what the cost of each one will be (no need for great precision, but to have an idea).
This is the only way that allows you to really choose. Otherwise, it is not you making the decision.
Back to the tools thing: if I know I will need to cut some wood for this project, I know I will need a tool for that. I consider all the wood-cutting tools, put in balance the price, how easy is to find the tool (do you have to order it?), if I know how to use it, how long will I use it, what is the productivity with the various tools.
And then I can wait with the real decision until I find out more.
I can even do the decision in steps. In two days I will have to decide if I order that chain-saw from Japan. If I decide not to buy that, I can wait two more weeks for the other sub-decisions, because the other tools are available at Home Depot.