Pruning a new Cherry Tree

[GardenerGirl]

I ordered a dwarf cherry tree online, and it just arrived a few days ago. I planted it immediately.

In the planting instructions, it said to prune branches back to around a foot long each. But when I unpacked the tree, it was already started to bud and flower, with a fair amount of new growth on each branch.

I've heard it's generally not a good idea to prune while the plant is actively growing. How long should I wait? Should I leave off the initial pruning entirely this year and just prune it back in the fall or early spring of next year?