Do plugins have a 5000 record count limit & 2 minute timeout limit?

I'm building a rollup query based on a link I found for a client. The client has over 10,000 opportunity records. Should I use this method here:

http://mscrmshop.blogspot.co.uk/2012/04/how-to-update-parent-record-when-child.html

I am concerned that developing the plugin this way will be limited by the 5000 page limit and or the 2 minute execution timeout. I am intending to have the plugin run asynchronously. Any help is appreciated.