I can't recall ever having to wait much more than 5 minutes for a shuttle to the 'nest' from T4; most delays are on the airfield, there may be none or several.

The main issue is that whenever there's an aircraft movement near the bus the driver has to stop and wait. This often happens more than once as the bus heads from between the T4/T5 piers, out onto airfield, up past T5, T6, T7 & T9 and then back to the 'nest'.

That is why the time to get ot the 'nest' can be so variable.