The stop times for each chassis and location (normally the pit lane itself) will be confirmed by the divisional moderator before each race.
A timed pit stop must be taken between 1/4 and 1/2 race distance (the second quarter of the race). The moderators will normally allow the maximum leeway where the number of laps does not neatly divide by four.
If two timed stops must be taken, the second must be taken between 1/4 and 3/4 race distance, and not on the lap immediately following the first stop.
Regardless of where the start/finish line is with respect to the pit lane, taking a stop is regarded as being done at the end of a lap.
For example: the race is 27 laps; stops must be taken no earlier than the end of lap 6 (27 divided by 4 and rounded down) and not later than the end of lap 14 (27 divided by two and rounded up).
It's generally easiest to reckon in terms of laps to go; in the above example, the pits would be open once the lap board read 22 (27 minus 6 plus 1) to go, and the final lap on which a pit stop could be made would be when the board read 14 (27 minus 14 plus 1) to go.
For divisions allowing fuel stops, a fuel stop cannot be combined with the compulsory timed stop(s).
If you are forced to Shift-R in the pit lane during your compulsory stop (eg. if you crash) you should SnG within 2 laps as usual for a 'fault' Shift-R.
A corner or two before the pit entrance, issue a "Pit In" message.
If another driver is close behind the pitting driver, the latter should consider moving offline and/or raising an arm as a further warning to the other driver.
If the driver misses the pit entrance or fails to stop within the pit area, they must go around and try on the next lap.
On entering the pits, the driver should stop in the pit stall area, not on the entry/exit lane. Normally the pit stall area is marked by lines but at some circuits there are several sets of lines (Mexico) whereas at others there maybe none other than the pit lane marking itself (Albi). In general cars must stop within half a car's width of the stalls regardless of the presence of stall markings. The moderator may decide to penalize a driver who gains an unfair advantage by not stopping in the appropriate area.
Drivers are not required to stop at their own pit stall; they must however stop within the stall area and in a position which does not hinder other drivers who might be trying to enter or exit the pits.
If another driver is already in the pits, if possible the pitting driver should stop behind them in case they move off or creep forward whilst the second driver is trying to find a stall to stop in; if the pitting driver must stop ahead of another driver, the pitting driver must leave enough room for the stopped driver to creep forward a few car lengths.
Drivers are advised to keep the car in first gear, with the clutch disengaged and the engine revs held at a medium level for the duration of the stop. This minimizes the risk of GPL retiring a driver, and is especially important for drivers taking long stops of 30 seconds or more.
GPL will retire a car which is stationary for 30 seconds, so drivers doing stops of that time or greater should move forward approximately four turns of the front wheels, using medium to high revs (effectively a mini-start), midway through the stop.
Shortly before exiting the pits, the driver should warn other drivers that they are about to leave by issuing a "Pit Out" message.
On exiting the pits, drivers should (where practical) stay off the racing line until back up to racing speed.
Drivers are reminded that they can see only one car behind in their mirrors when racing online.
Paul Harrington has written a very useful utility called GPLWait which allows you to set up two keys, one of which types a "Pit In" message for you, and the other which does the following:
Presses F10 (switching the view and providing visual feedback that pit stop timing has begun.
Typing a "Pit Out Warning" messages 5 seconds before the end of the stop.
Typing a "Pit Out" message at the end of the stop and pressing F10 again, switching the view back to the original setting and providing a visual cue to exit the pits.
Download keyhook.dll and the latest GPLWait zip file from the Pitstops directory of the shared files. Unzip the contents of the zip file somwhere and put the DLL in the same place. Then just run GPLWait.exe.