What can anyone tell me about "none too soon"?

It’s the use of none to mean "in no way" or "not at all", same as in "none the worse".
So it means "not at all too soon". By denying "too soon" it gives the meaning "very nearly late", and qualifies as litotes, Brad’s WotD for 1st October.

The construction "none too" used in this way is first attested by the OED in 1885.

Grant

Ahh, thanks Grant. It’s not lost on me now. Uncanny you mention that it’s a litote…"none too soon" popped into my head while perusing Brad’s litote WOTD string, but curiously enough was highly unsure of its meaning. Pure intuition.