at 10p every 4 hours, or there abouts, so under £1 a day I would just leave it running personally, and make sure it doesn't get too cold in the boat and it'll be alot better alot quicker! Also keep open all doors and lockers to aid air flow and get maximum effect.
That's certainly how I tackle boats when that approach is possible. It's not a huge expense but makes a big difference, and one it's been on for a few days go and scrub down all the surfaces and bulkheads and she'll look like a different boat.
It depends how much you want to spend. I put mine on a timer having it switched on for 12hr/day, normally at night on the assumption that a little bit of waste heat will do the most good then. The boat seems fine and we leave bedding out ready.
I leave ours on constant, but it has a humidistat. In winter (in Wales) it would almost certainly be full when I get to the boat. In summer, after a couple of weeks it might be only half full. No damp at all in our boat.
We did a 50% duty cycle in Pembroke split into 4hrs on 4 off - definitely needed to bypass the collecting bin and send the water straight down the sink. Make sure if it overheats you wont set anything alight. Do remember to block up all your boat vents (plastic bags or similar) or you'll be trying to dry the planet!!
We found it best to leave the unit on - so long as it has a setting for humidity control. It will sometimes go for days without actually triggering. It is best to get one with a hot gas defrost as this will enable it to work well when it gets cold. A good unit we bought was this one (no affifliation) Dry-it-out
It is a bit fiddly to get a pipe to drain it into the sink but thin surgical hose worked OK.
You can overdry the interior! If you go to the boat and the doors and boards are warped then you have dried her out too much. I have found that I only need to leave mine on Dec; Jan; Feb and even then turn the humidistat down. For the rest of the year it is pretty good when you have had a foul day in the rain and the interior is festooned with wet foulies. Put the unit on full chat and spend six hours in the bar.The gear will either be dry or you will be too plastedred to notice or care.