Your post is a little difficult to respond to. The fstest way to get to Arenal from Jaco is probably by road (flying may be an option) and that will be about 4-41/2 hours whether you drive yourself or hire a driver. It is another 1/2 day from Arenal to Monteverde, at least.

It makes no sense and may not even be possible to do both Arenal and Monteverde with only an overnight. Stick with Arenal

If you want to go to that area, then leave Jaco early so that you are in Arenal by about noon and plan an afternoon activity, try to see lava flow at night and do other activities the next day. You will not be bored in Arenal. Keep in mind that the volcano may or may not choose to show itself.

I am not sure what places you are talking about arranging admission to: Monteverde is a town and Arenal Volcano is just that with either visibility from the town of La Fortuna or the stretch of road between La Fortuna and Lake Arenal. What were you planning on admission to?

you are trying to squeeze in too much

if you have a couple spare days hire and driver and spend them in Arenal but I wouldn't drive it for a day trip

Arenal or Montevere...no two of them...

Luis Road Advisor

Just buckle up and enjoy the ride in paradise!!