Select the inlet.
Open the Boundary Conditions quick edit dialog in ONE of the following ways:
Type = Temperature
Units = Celsius
Time = Transient
Time Curve = Ramp Step
On the Time Curve dialog:
T1 = 10, T2 = 20, T3 = 30, T4 = 40
F1 = 500, F2 = 300
Click OK.
Click Apply.
For more about transient boundary conditions