wincc Symbolic I/O assistance

Could anybody walk me through this problem, it is driving me insane.
I want to have a text box that is used to set the value of a timer. But I want the options pre-defined. So the operator can only choose:
1s
5s
10s
30s
I have had no success getting the required value written to the necessary timer, could anybody shed a little light on this for me?

Thankyou.
(I should mention the HMI is a TP177 Micro and WinCC is Flex version.)

I would setup a text list showing the time value. When each time value is selected it would set a different value to an int variable. Then in the plc look at this int varaible and move a value into the timer. I don't think you will be able to load a time value directly into the Timer from WinCC Flex.