My non medical answer is I’ve never taken that drug, but I one time took an SSRI and I knew I was taking the drug right away. It was not a good drug for me. Still, my point is it didn’t take long at all for me to feel effects from the drug. Most of my friends who have taken antidepressants feel the effects very quickly. Good and bad.
Do you remember how long it took the first time you started taking it? I would guess it wouldn’t be much different this time. Maybe a little faster. That’s just a guess on my part. I looked up the half life and it’s 36 hours according to Wikipedia, so it’s probably completely out of your system now, and probably doesn’t take very long to build up and stabilize when you start taking it.
Next time, if you know you might have to go a few days without a new prescription, you might want to cut your dose in half if that’s possible for a couple of days (so you can have 4 half dose days rather than 2 completely without) to get you through. I don’t know if it’s a pill you can split? I don’t know what it looks like. I realize you might not have known you were going to have to do without, I don’t know your specific circumstance.