If Germany "blitzed" by sending in 1 tank a week, I dont think it would have been very effective.
If a football team only sends 1 player on a "blitz" they probably arent going to do much.
I think the use of "blitz" implies multiple in rapid succession. If its every other day I could still consider it a "blitz" but if its 1 per week, thats a trickle.