Might I suggest you make a new thread, sticky it, and post the people that are expected to show up and ready to raid for your time slots?

The stuff I do is totally ad-hoc. We just grab anyone who wants to go / core people and knock *something* out.

But your approach is much more structured and formal, so why not treat the roster the same way? If people can't make it - at least you could have notice about what you need to PuG / grab from the guidies if people want to go.