When is a good time to start an extension?

[Lisaturtle]

Considering a 2 storey extension and discussed with architect. The cost will be at least 100k realistically (house is stone). I have a 3 year old and a 14 week old! I am no stranger, at all, to the enormous psychological impact of building work as my parents built their own houses. We have lived in this house while renovating it too. Therefore I ask you, when did you choose to begin?!

What factors made a difference to you?
Children's ages? I don't want to entirely unsettle them especially as one is starting Reception in September
Financial climate? in light of possible recession will it be more difficult to get the work done?
An absolute need versus desirable space? We aren't desperate for the space yet and no time pressure to complete it.
Is it better to start when I'm back at work and not on mat leave?

I moved into an old house with an awful dark little kitchen without an outside window.
I had plans done, finally got planning approval after about a year, and then booked the builder for the following April. I had no desire to spend winter with a three walled house. The work was finished at the end of July.
My ds was 7, so old enough to not fall into the foundations and to understand that he wasn’t allowed to play with the cement mixer.
Financially, I started when I had a good job, and had saved half the expected cost, then was made redundant half way through but had a good payoff, so was able to finance most of it that way, and then paid the last little bit (the budget over-run) once I’d started a new job.