Would suggest you leave Sydney till the end of your visit. Air is thick
with smoke in the centre of the city, so even if you didn't intend to visit
the Blue Mountains, it could be more pleasant in a couple of weeks time.
If you only wanted to spend time around the city, harbour and surf
beaches, and changing your itinerary will mean missing the tennis or
less time in Sydney later, then you may as well stick with your original
itinerary. Sydney is a vast city (80 km from North to south) and
stretching inland 50ks or so to the Blue Mountains, so there is plenty
to see and do without venturing anywhere near the fires.