It's probably because its pushing your processors harder now so it's hitting the fault faster.
In my case I'm now seeing almost a 4x increase and it will work on the long run for 15 minutes... If you were using 4x less processing power it kind of makes sense that it would last around an hour until it hit the fault.
Re-mined every hour?
Who has time to operate this way?
There have been numerous posts explaining how to create a simple batch file (windows) or bash script (*nix) to continually restart the miner if it crashes. Just check back through the last few pages. This means that you can just leave them running, and they will restart straight away if they crash.
Without success, to ask specifically how to operate, thank you!