Hi Geecee68,
I’ve only just seen your message, so apologies for the late response. Yes you can filter through at the frontier, I would plan on arriving after 10 am and before 11 am if possible. The reason being is that between those times the rush hour works traffic has largely gone through, and the tourist traffic has is only just starting to pickup, plus after 11 pm the schedule airport landing arrive, so affectively closing the road in and out for 10 minutes or so, causing more delays.
Motor bike parking, if it was me, I would park in the ICC car park, the entrance and exit are on Line wall road, just after the mini roundabout and the petrol station. It’s a steepish ramp up with a bend at the top, so carry a bit of momentum going up. The bike parking is right next to the kiosk. After you’ve parked up, walk up to the next floor and get the lift down and you will be smack in the centre of town. If you’re planning on going up the Rock, then take the taxi tour, you have the taxi for the whole tour, and the price includes entrance to the caves ( well worth a visit ) also the siege tunnels likewise, the taxi will wait for you outside each place and take you to the next. Don’t even think about taking the cable car as it will only take you up the rock.
Enjoy Gibraltar, it’s a fascinating place...
Forgot to mention, to get your passport stamped going into Gib, as you are leaving the EU, and stamped again when going back into Spain to show that you have re entered the EU.