The group will be fastest when they ride
in one group of 11. With most of the time or all the time the 3 fastest in front.
The worst time will be at most
13 minutes 40 seconds
Proof
We know that
there is a clever energy preserving rotational strategy that works for 3 cyclists with time a<b<c such that the slowest time c is reduced to (a+b+c)/3
and common knowledge dictates that
larger groups should be able to preserve the same or even more energy as a result of energy preserving rotational strategystrategies.
Therefore
It must work at least as good for 11 cyclists.
We might go for the time by the top three cyclists
They could finish alone in 11 minutes.
But, we can not know
at which pace the slowest cyclists will be able to follow the pack.
Yet, we do know that they can finish in
at least in 13 minutes and 40 seconds, because the slowest cyclist is able to follow at that speed in a group of three, so certainly as well in a bigger group.