On my wife's iPhone I would have probably been cutting it too close for comfort to get the Barn Owl or would have just fallen short somewhat. What I did was to use a decent bit of the freely acquired gems and speed-hatch several of the animals that were in storage there. I sped a Goblin Gobbler, the Ra, a bastet and something else I don't remember off-hand. It's a really handy and useful way of spending gems towards securing the owl.
This way these beautiful animals were finally hatched and started getting productive, as the cash income on that installation doesn't go all that fast, which is a major bottleneck for expansions, causing precious bombs to get lost because the rune amount has been met well before there's enough cash to expand...