[throw_a_grenade]

You just set limits on everything (time, buffers, ...), which is easier said than done. You need to really understand your libraries and all the layers down to the OS, because its enough to have one abstraction that doesn't support setting limits and it's an invitation for (counter-)abuse.

[starttoaster]

Doesn't seem like it should be all that complex to me assuming the crawler is written in a common programming language. It's a pretty common coding pattern for functions that make HTTP requests to set a timeout for requests made by your HTTP client. I believe the stdlib HTTP library in the language I usually write in actually sets a default timeout if I forget to set one.

[Calzifer]

Those are usually connection and no-data timeouts. A total time limit is in my experience less common.