@JMichaelTX’s solution is the right idea, but it is generally better to use the function NOW() or SECONDS() functions or rather than %ICUDateTime%A%. For one thing, the ICUDateTime solution would fail if the macro ran past midnight.
SECONDS() gives you the number of fractional seconds since the Mac started, so for timing a duration, it is probably the best bet.
Use Set Variable to Calculation rather than Set Variable to Text to work with functions.