Timing out fopen using https stream wrapper?

I have a class that uses fopen to read some xml data from a site with ongoing stability issues. Fopen is using the stream wrapper for http. Something I've struggled with is finding a way to set a timeout value when fopen is attempting to get a page from a site that is inaccessible for some reason. On my test server, the behavior is that fopen seems to hang up, and the script never returns. It seems I have been over the documentation repeatedly, but there simply isn't any documented way of setting a timeout duration. Any ideas?