The optimal length is enough to bind joke-hova, no more and no less. How long does it take to say a prayer that effectively binds joke-hova instead of praising that thing? Otherwise, prayers are simply donations of psychic energy to joke-hova for the purpose of enslaving mankind. The longer the prayer, the greater this donation, and the more effective joke-hova can be in imposing communism, slavery, and a dark age on us all that, this time, there is no hope of a Renaissance.
The best thing is to simply blow off such prayer. Especially the last one. People walking out of the place at the start of the prayer (even better, as soon as the concluding song is announced) would limit the donation of psychic energy to joke-hova. Even better would be not showing up at all--I noticed that I was always drained worse from sitting at a big boasting session even than going to work for the day. The whole thing is nothing more than a donation of psychic energy, along with indoctrination and programming of your soul to accept damnation.