No wonder you got "lucky." Hope you have enough water to get kayaks and I.K.'s down. You're almost going to have to pray for rain right before you launch.
I've done 16 bridge-to-bridge Salt trips now, and with the flows you're going to probably have, 5 days is going to be tough, 6 would be better, unless you just want to spend all day each day getting down the river, with no time to enjoy camp or hiking, etc. There are some great hikes down there, and it's not worth rushing the trip.
Have done it at all flows, from 800 at the put-in to just over 8000 at the put-in (had just over 18,000 the day we did Quarzite and the canyon below: full-on yahoo). My vote would be anything less than 900 at the put-in isn't worth bringing rafts for, but I'm guessing other who are willing to abuse their gear will disagree
There are a lot of great camps, use your own judgment. Make sure to camp on riv left if you stop anywhere before the road ends. Less hassle.
Canyon Creek is a "must hike" stop. Too beautiful to miss. No camp there anymore, unless you're a marmot
But, there is a tough-to-find and hit camp just downstream on riv rt, tucked up in a little draw. It's the only way to camp near Canyon Creek and hike back to it to do a long hike up the creek. Worth the carry up in to the draw.
I would also say do anything you can to avoid camping on or near Gleason Flats. There's a great, more or less "new" camp on river left about 3/4 mile before you get out of the granite canyon above Gleason Flats, a bit of a carry uphill from a cool rock island. See pics attached. It's just downstream of Ash Cr. on the left. 30 min of rowing into a headwind the next morning brought us out into Gleason Flats, and it was a much nicer camp than being out there with the ATV's and cowshit. Get across Gleason Flat and thru Eye of the Needle and Blackrock that day, then find a place in the canyon before Quartzite. Several very good camps in there, but beware of side canyon flash flood potential.
Latest I've ever launched is April 17, and have bagged two trips that would have launched earlier than that due to low/no water. Can't imagine what you may be looking at on May 5. PM me if you want more details on a good, cheap shuttle and car storage, etc. Good luck.