You just did. The better question is “why?” What are you trying to accomplish?
Again, the answer depends on what you are trying to do with it.
See, for example, my rule to call another rule if a contact sensor detects that the Litter Drawer has been open for 30 seconds on the Litter Robot, which needs to measure elapsed time in seconds.
If you are trying to get the current time to display a clock on a Dashboard, remember that the Dashboard only refreshes every so often. There are examples of clock displays in the forum. Just search.
RM will show you the available choices in a drop down.