[S7-300] Basics, how to use time and date?

Hello

I have simple home automation made with Siemens S7-300 series. It consist of CPU 315-2 DP, Digital inputs (321),outputs (322), relays and light switches.

Currently I control lights and some doors with simple code (STL), such as:

A "I 1.1" (switch 1)
= "Q1.1" (door 1)

or

O "I 1.1"
O "I 2.1"
= "Q1.1"

I would like to use time or date based controls, but I don't know how to do it.
Time and date is correctly set from Simatic Manager.

Is there any "variables" that can be used to check time or date?

Something like:

IF time_variable > 08:00 and < 10:00
= "Q1.1"

Here's a link to an example project that uses the time and date.

http://www.plctalk.net/qanda/showpost.php?p=348443&postcount=2