It counts the number in your hand after playing it, so if you have 3 or fewer cards in hand before you play
Servants to Saruman you'll get +3 strength. Basically, between announcing that you'll play the card and carrying out the effects the card is in "The Void," the place for cards that aren't anywhere. The effects of the card happen while it's there. On the flip side you need at least 5 cards in hand to get the damage bonus from
All Save One since with just 4 you'd lose initiative in the process of playing it.