To follow-up on lantere's response, if you want to control how the result of the calculation looks, use:
& TEXT(F23/E23, "0.00")
TEXT will accept a variety of number formats - just like cell formatting of numbers.
You can also continue your message like this:
="Average cycle time is " & TEXT(F23/E23, "0.00") & " seconds"
which gives you:
Average cycle time is 150.00 seconds