In BA on the 747 we tend to put in TOC wind and then a couple or so waypoints later the average wind from the flight plan, much as Old Smokey suggests. That will get rid of 'insufficient fuel' messages and give reasonably accurate ETA and Fuel Remaining numbers right away.
On reaching TOC the PF goes 'head down' and updates the en-route winds/temps as necessary. That can take as little as 5 but as much as 15 minutes (or longer in the early days). The rule of thumb is for entering changes seems to be 30/3, ie input a new value when the wind changes by 30 degrees or 30 knots, or the temp by 3 degrees C.
Personally, I try to put the winds in to the Oceanic Entry point before departure if I can, else I just add the EET to that point when firing off the ACARS Oceanic clearance request in the climb - works well.
Hopefully in the future we will be CPDLC-able and get the flight plan and winds etc uploaded as the 777 does.