@likavoss
If you aren't worried about delivering the cargo, you can just have someone collect it and leave it. The cargo portion of the voyage is considered complete once you take it all from the person that has it. There is no need to actually deliver it when it comes to completing the voyage.
If you aren't worried about turning in the chests, you can tap them with your shovel and leave. Those portions of the voyage are completed once the chests have been tapped but you don't have to completely dig them up or even turn them in.
The order of souls portions will take the most time and effort, especially if you get gold skeletons on a large island far from the water. Bringing kegs could help save time in certain situations like that one.
I would suggest doing devil's roar athenas for various reasons. Being in the devil's roar means you are only getting islands in the devil's roar. If you did a regular athena you could possibly have to sail from shark bait cove to old faithful island. Devil's roar voyages won't be as spread out which saves time in travel.
Skeletons can easily be taken out by geysers. With a little bit of positioning and timing, you can kill entire waves without even touching them. That can potentially speed things up tremendously.
Ashen villainous skulls are pretty expensive for a common item. Even the ashen captain's chest are not that bad. If you do decide to keep the treasure to turn in, you'll make twice as much on it than if you were doing a regular voyage.
Doing a solo athena could take over 2 hours easily if you are collecting everything and don't plan out a smart rout to take between islands. That's with trying to be fast and efficent. Having someone with you to fire themselves off onto islands to tap chests and collect cargo can save tons of time while you continue on to the next objective. If you ignore cargo and tap all ten chests, that only leaves the eight captains, so you will only really be stopped at two islands spending time on the voyage. If you get REALLY lucky, all eight will be on the same island. If you ignore most of the treasure, with two people you might finish in a little more than an hour depending on location of islands, wind direction, etc.
I would always make sure you have plenty of time to finish because you could sink for whatever reason. Other pirates, kraken, even floating barrels. Losing your ship will slow you down. You might get respawned at the other end of the world. Another advantage of being in the devil's roar, your new ship will spawn in the devil's roar.
Also, always and I mean ALWAYS have a lifeboat. I mean rowboat.