Hello. I just wanted to know if there was a way to adjust the speed for Roller Coaster Tycoon Deluxe Edition; I've looked about but I can't seem to find it, if it exists.

There isn't any such control. And slowing down the game by keeping the computer busy doesnt work with modern machines anymore.

I don't understand why anyone would want to adjust the speed or slow down the game when the player can just... pause the game.

Rollercoaster Tycoon (Deluxe) is a 'pause & play' game.

I'm most interested in the park designing and running part of the game, not so much fancy coasters and decorations. A park that can run unattended for a long time without developing problems is my idea of perfection. With the aging mechanism invariably wearing things down an overnight test run is a bit long on full speed, but if its "overday" I can't restrain myself from tempering, defying the "unattended" part. Half speed for 8 hours would be just perfect.

Thats what I'd like time controls for anyway. But the time difference between designing a ride on the fly over the course of a game year and dropping in a prebuild in a second seems more like an unfortunate side effect than a tactical decision as well.

I enjoy the park designing and micromanaging the business portions of the gameplay myself, however, a time control function removes the skill-based part of the gameplay in Rollercoaster Tycoon. Part of the fun in the original Rollercoaster Tycoon is knowing when & what function allows the player to pause the game to place a building, or knowing the science in tweaking the details in your marketing campaigns or how much money to borrow towards funding a project inside the park.
I am confident that a time control function was intentionally left out for the purposes of the pause button.