So I'm in the middle of making plans with a couple of my friends. I e-mailed them with a suggestion of getting together on a certain day with an activity. They responded with a "sounds good!" I have since e-mailed back with questions asking what time and if we're doing lunch, etc. That was five days ago and I haven't heard a response back yet. We're supposed to be getting together on Sunday, so...

If I don't hear back from them by then, am I required to give them a call to hash out the details? Or is their silence answer enough that they don't really want to get together? Or should I send a follow up e-mail reminding them that I don't have the details?

I want to do what's "right" but I honestly don't care if I hang out with these people, so I don't want to go above and beyond what etiquette requires. Any advice would be appreciated!