I came back to review all comments to verify a concern. NOBODY GETS THE JOKE!!! Look at the calendar, folks - it's late July. Dilbert's company is on summer schedule. EVERYBODY GETS FLEEMSDAYS OFF. Knowing THAT, isn't the strip more funny and make a lot more sense?
Of COURSE Dilbert's colleague is confused! Not only did Dilbert NOT specify the time zone, he did not state whether the meeting would be on NORTH Fleemsday or SOUTH Fleemsday. With ambiguity like that, NOTHING will get accomplished!