EDIT: I wrote this guide back in the day when there was absolutely no way to skip the waiting time for the Extreme mode (yes, I afked the whole way, fun times), and I provided my save file for easy unlocking of the achievement.

Now, there is a built-in function to skip those pesky waits using a secret keyboard shortcut that appears after you have the 'Help' screen open for around 30 seconds while playing the Extreme mode.

Spoiler: Whenever you come across a wait timer, press the keys Shift+Alt+H to instantly reduce the timer to 5 seconds.

I'm leaving the rest of the guide here for posterity, though you may find that the save file no longer works as the latest update broke the loading of old saves.

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About

Unless you have been living under a rock, you should know that the latest game update has brought the total wait time for the Desert RV achievement down to 12 hours (from 170 hours previously).

For those of you who are true masochists, you can still unlock the achievement by idling the game, but for the rest of us, I am providing my save game that you can download here[anonfiles.com], here[www56.zippyshare.com] or here[gofile.io].

Usage

Once downloaded, you may rename the file to occupy an empty save slot in the game. For example, my save was in slot two of the first save page, thus it is "1-2-LT1.save". If you renamed it to "1-3-LT1.save", it should occupy the third slot instead.

Next, move the file into your game save folder. On Windows, it should be at C:\Program Files (x86)\Steam\steamapps\common\Highway Blossoms\game\saves, unless you've changed your installation folder.

Run the game

Self-explanatory.

Load the saved game, and wait for a minute (literally). The achievement should unlock when the timer's up.

Footnote

I must add that I completed the game (i.e. unlocked extras) before attempting to get this achievement. No warranties are made if you try to get this achievement before doing so.

WARNING: Remember to backup your save files in case things go awry.