Well, that's a complex question, which is a lawyerly way of saying I don't really know. My understanding is that they are burst-transmitted automatically whenever a transmitter becomes available. Needless to say, transmitters are much harder to find than receivers, so we have to be more opportunistic about using them. I'll ask Dilyn to answer this, but I don't know that she'll be in again today. It's reasonable to assume that the probes will "hear" you, though, if you manage to add your upload by 10:00 AM EST on the day of the download. That isn't always going to hold true, the probes and transmitters often do their own thing, but it is a good rule of thumb.
Does that help?
I've got to run, but I'll be back later. Glad to have you with us!
*Nimrod*