[sokoloff]

Purging the lines is done to eliminate moisture and other non-compressibles. The 24-hour standing vac test is a way (but not the only way) to prove a lack of leaks.

Particularly if you're going to flood with nitrogen (as the pros commonly do) and do a positive pressure decay test, there's absolutely no need to take overnight IMO. Taking overnight is a compensation mechanism that DIYers use to avoid buying the N2 bottle/regulator (which the pros already have because of their need to braze every so often).

I think DIYers can get as good a result as the pros, but I don't think the 24 hour vac test makes for a better result than a methodical pro will get.