"For pilots, how much time do you need to enter the details into the FMS for a hold that isn't on the flightplan "
- 5miles - for any en-route hold, as much notice as possible please. We can (737) hold 'at present position' almost instantly, but if an arcane entry procedure/route is specified, we need a minute or so to enter it into the FMC, more-so when the points are RNAV waypoints rather than VOR specified. Even an 'unusual' hold on the arrival can cause a flurry, and when, as has happened in the London arrivals in my experience, the hold given is not on the chart/route we are using for the cleared arrival, there will be some frantic paper shuffling too! Don't forget that all changes to the FMC/Nav plan should ideally be 'run past' and accepted by the other crew. Any advance warning you can get from TC or from what you can see in the inner stack levels will help - eg 'expect to hold at Pompi', and if the hold is non-STAR based, some guidnace on how YOU want us to get there is useful, rather than our having to guess and finding out we are wrong!
"Also for the pilots, does it annoy you once we get you to enter an unusual hold (ie. off-route) and then cancel it just as you get there? It seems to be "Murphy's Law" that we always do this!"
- yes, but we are all big boys and girls and can live with it
. Preparing for such an event will have caused quite a lot of acivity in terms of setting-up the hold, reviewing fuel/div options etc, talking to cabin/company/pax as appropriate, but it is always (normally) good news when it gets cancelled.