In my experience, the end date is not important, because you will get a visa for much longer than what you expect. The beginning, however, is very important. Your visa will start exactly on the day indicated on the voucher.

In response to your other question about your expiring passport… the visa will be valid to the day your passport expires minus 6 month.

And about registration… when you arrive in a hotel, you will be registered for either free or for a nominal fee of a few dollars. I usually collect the registration papers, but no one ever, ever demands them when I leave Russia.