Yeah. The right time to exercise when a company is filing is like...a few years before, when the shares were pretty much imaginary and you weren't standing to be taxed for imaginary wealth (why I once agonized over buying 25 cent shares for 700 bucks in a company 4 years away from an IPO, I have no idea--it's either lost money or free cash. Assume it's lost money and you're either right or happily surprised a few years down the road; both aren't such bad outcomes).
You've likely heard this, but one thing you might want to look at is a hybrid transaction (I think they call this a "cashless transaction"); exercise and sell enough to cover taxes and to purchase anything you've got available to exercise (to hold for another year).