So I'm arriving on QR 702 which typically arrives earlier (around 4:30pm), I'm curious if I can make the 6pm tour? I can book it online in advance to secure the spot but just want to check if it's at all possible. I'm flying in J so security check should be quick.
Additionally, I will have a piece of carry on roller and backpack, can I store the luggage in the lounge or does the bus have a luggage storage space available?
Looking at the recent history of QR 702, I think the chances of making the 6pm tour are slim. You have to check in at the tour desk 75 minutes prior to departure, or else you're considered a no show and I presume they can give your spot away. After you check in, tickets are distributed, which are collected after going through immigration. The process of going through immigration, led by a tour employee, begins well before 6pm, as 6pm is the bus departure time (from right outside of baggage claim). As far as luggage goes, it is possible to check it in the Al Mourjan (and maybe others?) lounge, though there may be confusion as to whether this is allowed or not, so I would try not to draw too much attention if I were you. You can store your luggage on the bus, but if it's bigger than a small personal item, like your roller probably is, it will likely be put underneath.
I recently took the 8pm tour after arriving on QR 778 and found it to be a great way to break up a long layover.