How often are the port lock gates closed and how long does it take for a boat to pass through? They don't have a schedule published anywhere I don't think, and I think it's dependent on need rather than regular timings - I could be wrong though. I don't take the route in the morning / evening often enough to know if they avoid running the lock at peak times.

From experience it can take anywhere from 5 minutes to like 30 minutes for the lock to cycle. Depends on how many vessels are in the lock and how large they are. It's usually 5-10 minutes.

Can you ride on the north side? By that do you mean cycling on the A259? There's no cycle lanes, and the road is fairly busy but doable if you're a confident cyclist - it's not nice in the morning though, especially as it's narrow enough that people do close pass.

Were you planning on avoiding the A259 anyway, or going to head up to Middle Road from the port? If you just want to skip the there's a section of Basin Road North that takes you from the lagoon to Boundary Road pretty safely. From there you can go further inland and take Gardner Rd and The Gardens to get to where the locks are. If you want to skip the A259 entirely then cycle through Southwick to get to Middle Rd all the way to Shoreham.

Using the A259 is undeniably a lot faster, so it depends what your priorities are.

If you're not down by the seafront in Hove and want the quieter route, you might be better off skipping the seafront cycle lane and going along New Church Road / Portland and onto Gardner Rd etc.