A large number of troops typically schedule these on Sunday mornings, to make up for the fact that they are keeping their scouts from their worship services at their regular church.
From the BSA training Materials:
It is not necessary to attempt to account for the sensitivities of every conceivable religion on Earth; rather, seek to account for those religions whose members reasonably might be expected to be present.My rule of thumb is to be as inclusive reasonably possible. For example, if you know all the scouts in a particular patrol or troop are of various Christian denominations, it would be fine to reference Jesus in a prayer. However, if it is a larger group, and there may be people of non-Christian backgrounds there, try to be as sensitive as possible, and avoid putting them in an uncomfortable situation, while still respecting their faith.
Some faiths ask that it's members do not participate in interfaith worship services, and it is important to remember that. No Scout should ever feel forced to participate in an interfaith worship service, particularly when it violates the tenets of his own faith.
Before asking a Scout or Leader to run one of these services, make sure they are aware of some of these potential pitfalls. The BSA website has the outline of a training course for this, and I think it is something that would be very useful for troops and local districts to educate it's scouts and scouters about.