It's coming up on midnight in Israel so if we're likely to see an Iranian attack, it should come in the next six hours. Fox reported earlier that an attack was expected within 24 hours and that led to spikes in gold and oil.
If/when the attacks happen, look for more of that along with some bond buying and yen strength.
The judgement call will be evaluating how hard Iran is hitting and how hard Israel is likely to hit back. The recent round of rocket and drone attacks came on April 13 and began at about 1:40 am local time. It was said to incorporate over 170 drones, 30 cruise missiles and 120 ballistic missiles. Most were shot down and none caused any material damage.
Ultimately, that attack and the response from Israel were more theatre than true efforts at retribution but these things can easily be miscalculated.
The market wasn't super quick to sort it all out as it unfolded over a number of hours, including some intense risk aversion for a time. By the time Europe came online, the reversal trade was in force. Given that we've seen the playbook before, I'd expect it to reverse more quickly this time.
Again, all that's conditioned on a lack of bloodshed. If there is some real destruction, then it's much safer on the market sidelines.