How long can I expect my cat’s first-ever FIC/FLUTD flare to last?

Hello, my 8 year old neutered male starting showing signs of urinary issues on 8/27, it was mild and I confused it with anal gland issues at first. On 8/29 (yesterday afternoon) when I noticed a few back to back litter box attempts and one with no production, I took him to the ER. He was diagnosed with FLUTD and likely FIC. Urinalysis showed some blood and struvite crystals, X-ray showed no stones, and he was not blocked/his bladder was empty. Still waiting on culture results but no obvious signs of infection.

Since being home we have started him on urinary prescription dry (mixing his old and new kibble) and prescription wet food. Also giving him gabapentin to keep him comfortable. Yesterday, he was staying in the box for minutes at a time straining, and aggressively licking his genitalia after each visit. Today I am seeing less straining while in the box, but still frequent trips to the box with small amounts of output. I am also seeing less licking of his genitalia. I am regularly checking his bladder area for tightness but his belly has seemed soft and normal. The vet said flares usually lasts around 5 days, but I am getting worried as we will be gone on a trip Fri-Sun (wedding that I’m a bridesmaid in). Friday would be day 8 after initial symptoms so I am reeeeallly hoping he is stable and urinating normal by then, but I can’t help but worry this won’t be better by then. We do have a rover scheduled to drop in Saturday and Sunday mornings.

I want to ask if his progression seems normal and if there’s anything I can do to ensure he stays on a good path to recovery. I also wanted to ask if it’s ok to feed him a Delectables Lickable treat once a day to increase moisture intake?