Smiler, I haven't been doing this long really, but anytime I have worked as a sub contractor or through another trade (which I no longer do and just stick to private work), its always "a small job" or "just a days work", mainly because the builders etc or perhaps your plumber mate who would otherwise do it themselves, don't know how to do it properly!
Yes it will take half the time if I put 60x30 porcelain tiles on a freshly plastered and painted wet room wall using tubbed adhesive (dot and dabbed of course) and grout it on the same day! The thing is, we know better than that and rushing these things is just no good. If it was all about speed, my business would have been over before it got started. I have gotten naturally quicker over time, but not because I'm trying to force that. I like to book out an extra day or two for each job (depending how big it is) allowing me not to feel under too much pressure to hit a certain deadline. Fair enough, that costs me potential income, but the stress it relieves is well worth it. Time is not everything.....