Considerably, it depends on the player.
Considerably, it depends on how aggressive the opponent was/is.
Considerably, it's your territory that counts.
(Not to mention if there is an Instant MP ability like Blitzkrieg)
Considering all factors, the player could be trying to defend his own ass from tanks the opponent built ages ago.
You know often I use a similar strategy. I send in a couple of StuGs that I've had for about 4 minutes just waiting for true deployment, in the mean time I'm making Panzers/Panthers or Doctrinal Tigers.
It catches the opponent by surprise.
"HA! I GOT YOUR STUGS! TIME TO INVADE (:<"
"So you think."
"DUDE...HOW THE HELL DID YOU GET THE TIGER?"
"Skills.
"Balancers are 10 a penny"