I agree with DiveMe... better to allow more time just in case, but I found that it took much less time in general than the guide books say to get any where (and the roads to Hana and Haleakala weren't nearly as "treacherous" as they're made out to be). It took us half an hour to get from Lahaina to the Kihei ramp, and about 15 minutes to Maalea for our trip to Lanai (for 6:30 am), as we didn't encounter much traffic... but with all the people diving, fishing or heading to Haleakala at an ungodly hour for Sunrise... DiveMe's right... you can encounter traffic at strange times!. Both have free parking available, but the earlier you are the closer you can park. Rergardless, you can unload your gear then go back and park. It's all nice and easy.
In fact... funny thing about parking... everyone warns how expensive and hard to find parking it is in Maui... esp. around Lahaina and Kaanapali. It does get busy in Lahaina, but we always managed to park in a 3 hour lot on front st. and never had to pay for parking. Around Black Rock is another story. We wanted to do a night dive there, but parking at whalers would be quite a hike with gear down the beach. A guy at the MDS there told us of a lot, but we couldn't find one single spot... or one that wasn't reserved for guests. We could've dropped our gear, left me with it in the dark, had him drive back to Whalers and walk back and meet me... but after driving around in circles awhile we'd had it. So, thought we'd go to old airport beach (which was a nice little day dive)... but they close the lot when it's dark.... grrrr.... we brought the full tanks back and never did the dive.
Then when we got home we'd arranged for Kevin's truck to be left in a lot for us ahead of time (since we wouldn't be in and through customs until 2 am) We thought that so clever... wrong!... we paid almost $36 for parking at the Vancouver airport for about 6 hours !!! ...and they say Maui is expensive.... welcome home to Vancouver !!!!!