[mikesride]

Well...obviously for this couple that time is committed for...
I also have never attended a church service but, if you had asked me the same at a time I had a hockey game, a work commitment or a band practice I would have said the same... The team is not complete without me there (I'm the goalie) work...well that's work and band practice is a commitment I've made to four other guys that my voice, my bass and guitar will be there...
So while I cant comment directly on how important is church to these folks....the answer is pretty obviously very important.
I think the right decision is to pass on the job if you feel there will be many time conflicts like this.
That also does not make the OP a shady contractor....in fact its the opposite of such, a smart business man that once he understands the prospects expectations understands there will be somebody else out there that will be better suited to serve them on their terms.