We have just upgraded SCCM2012 R2 to SCCM R2 SP1 CU1 and we have notice it takes a very long time before the TS shows within a PXE boot has anyone had

That's a know issue with the latest service pack. When you simply set the available time of the deployment a day back you'll be fine.

Thank you got the reply and that has worked.  It there a list of known bugs with this update somewhere out there so I know what to expect?

At the end of the following blog post is a list with Known Issues: http://www.scconfigmgr.com/2015/05/18/how-to-upgrade-to-configmgr-2012-r2-sp1-in-your-hierarchy/

Thank you : )

As a follow on note, don't confuse that list with an authoritative list though. That's simply a list of issues well known to the community and person who wrote that post.

Thank you for the update