You didn't say where you're coming from? If HK, I highly doubt you will make it, going through customs then lining up for the ticket....
If elsewhere in China, ensure you are in fact arriving at GERS and not Guangzhou Railway Station. Assuming you are arriving at GERS, it should be enough time, if you know where you are going! You'll be ushered out with the throng on the right hand side of the station, passing through a bottleneck of a gate. One through, keep walking around past the metro underground exit towards the big Macdonalds sign you'll see. Keep looking as you walk to your left and when you see the sign for 'Shanshui Hotel' & the Kungfu takeout place, walk through the walkway there past 7-11 to get to the main entry of the station. You'll have to go through the X-ray machines again, once though, turn left and both the ticketing and gate for the d-class Shenzhen express trains are on this level. They leave every 10mins.
Sorry about all the weird directions- but you know what Chinese train stations are like! I'm now back in Australia, but you make me miss this station heaps!