If possible, you could take the bus departing at 14:20 from Shenzhen Airport to Guangzhou directly.

Alternatively, once arrive at Shenzhen Airport, you could take the shuttle bus Line 1(330)to arrive Shenzhen Railway Station firstly in 50 minutes. Here, you could catch a bullet train easily to get to Guangzhou in 70 minutes. You could find the train schedule at https://www.travelchinaguide.com/china-trains/