We here in WarpToMe are slaves to the incursion timer set forth by ccp itself. So what this means is that Incursions don't always show up on any given day/night. they just do when the timer set in the coding, randomly by the way, goes forth and populates anywhere in the known universe. So in short form to answer your fair question, No there is no certain day/night of the week where WTM begins or ends an incursion. Although we here in WTM do not actively go forth and end incursions before withdrawing mode has appeared, we do end them if there has been ample enough information to end the current focus and move to the next one. By the by, welcome to Incursions and the WarpToMe Family! Hopefully this has answered your question, if not please reply to this thread and anyone here can fill more in for anyone that has anything further.
ps: Incursions are a very nomadic thing. meaning we will always be moving no matter what. this is half the fun of being able to see new and exciting places and meeting people along the way.