Sentry gun setup speed is increased by 25% per level, with a base time of 7 seconds. This means setup with Crash takes ~5.5 seconds, and with Vegas 4 seconds. This skill does not affect Sentry Gun dismantling speed.
Welding speed is significantly increased, although the exact times are difficult to measure.
If both Techs are taken, where the area-of-effect overlaps, the effects stack.