Block a steam game from myself for a period of time

You can right click on a game in your library and select "Set Categories". When you do this, there is a "Hide this game in my library" check box.

If you then want to see the hidden games (to unhide them), click on the filter next to the search box in your library screen (the one where you can choose "Games"/"Installed"/"Recent" etc)

It's silly but you could encrypt the file system of that game, give the encryption key to a friend/your mum and tell them to not give it back to you until 'x'; be that you've done your homework or whatever you're trying to get yourself to do.

A better idea would be to look into how to increase yourself control.

You could always give your login details to somebody you trust such as a family member, who can then change them and agree a time when you can have them back.

I know somebody who did this and it worked for them, it is the best way to avoid temptation.

Just make it not possible to play a game within X amount of time. If you want to restrict yourself to play, the only possible option is to let it cost time to play a game (like installing in, or install steam, install game) etc. In this time you can rethink more than once to think of your choice and stop the install procedure.

If you really want to stop play a game and make it impossible, just install an old VGA-card in your computer and store it in your closet. Now it takes a lot of time to play your game (Okay, maybe Tetris or SimCity 1.) :)

Step 1: Uninstall the game.

Step 2: Find out how much free space the game requires.

Step 3: Install other software (or download media) until the free space on you HDD is less then the amount needed to reinstall the game.

This won't work very well if you have a HUGE HDD or if the game is tiny. However you could also uninstall steam, partition your hard drive with a "just big enough" partition and install steam on that partition...