If you bull**** about being able to meet the time and you're early, you WILL get vectored. (unless things are running better ahead of you)
If you are late you will either be re-calculated which could result in a self induced shafting or if they slow everything behind you everyone else gets a compound shafting.
If they give you a time that's un-realistic it may be to save extra R/T time (The controller knows you can't lose that much time and wants to know how many minutes to lose in a vector) or it may be just a tool that couldn't get into uni, has had nothing to do with aviation and doesn't understand what they are asking you to do (not many of these).
I think AIP says you can be a minute early, but that's hardly in the spirit of things is it? As a controller it's relatively easy to lose a bit of time, but gaining it when things have stuffed up is difficult at best and costly for airlines.
Would love you fellas to sit in with the flow or Approach or Arrivals (or whatever they call it these days)
WHEN IT'S BUSY, not when
PR (
) deems it acceptable for you to visit.