Unfortunately, Edinburgh is closed this year. Well, Princes Street is closed, Haymarket has a diversion, Western Corner has roadworks...

Normally 40 minutes would be fine, including waiting time for the bus. They go at least every 10 minutes, often more frequently. Now I would allow 50 minutes plus - and be aware that if your destination is anywhere near Princes Street you will be getting off the bus elsewhere or your further journey (whether by bus or on foot) may be impeded. But don't take this as gospel, you may have a good journey or you may get snarled up for way longer. It's so hard to predict.

If you arrive at a meeting late, just curse the trams and everyone will cluck with sympathy.