As a result of my recent research, I got the time efficiency formula at hand in case somebody's interested.
The formula is (0.9 + 90 / ( time ratio + 100)). It's derived from the ME formula, as it can be also written as 1 + (1 / ((time ratio / 50) + 2) * (1.6 - time ratio / 500). Time efficiency multiplier crosses 1.0 @ 800pts.
So for factory, it's Item base time * (0.9 + 90 / (facility time ratio + CT time ratio + 100)).
For reverse engineering, the formula is 4000 seconds * required decoder level * (0.9 + 90 / ((facility time ratio + bonus time ratio) + 100)), bonus time ratio is the extra ratio you get for your CT if you use higher leveled decoder than required.
For prototyping, the formula is Item base time * 10 * (0.9 + 90 / (time ratio + 100)).
Results are always round down (a.k.a FLOOR'd) as is expected.
As for basetimes, ammo is 800 seconds, simple items 2000, intermediate items 4000, advanced items 8000, light bots 12000, assault bots 16000, mechs 32000 and heavy mechs 40000.