Both L1 and L2 visas are linked to your blanket petition. Petition is another document, issued by USCIS for 1 year. You can't get a visa, which expiration date is longer than your petition expiration date. My petition was approved in August 2012, but I received it in fact only in spring (after more than 6 months). And then, when I received it, it took several more months to make final preparations for the movement, so we were able to get a visa for her only in June (which expired in August according to petition expiration) and moved to the U.S. right away after that.
And again, petition has been extended already, but I only received it in August, even though it has been extended since April.
And there's no consulate in Belarus. You have to go to Russia to pass interview and stay there in a hotel for about a week to wait for your passport to be returned.