Yes, there is an opening act. He's David Garza.
From what reports of attendees at this week's shows in Portland and
Seattle, it seems that Mr Garza's performance and soundchecks consume
approximately one hour.
From the Beyond The Rubicon Fiona Apple forum (registration required):
"what time did she come on stage and perform?
For the Seattle show the doors opened at 7, the show started at 8. I
have no idea how long Garza was on for because I went to get some
food, but by the time I got back to the theatre at 9, Fiona was on."
"Opening for Fiona was Davíd Garza...
He did around five songs but for the life of me, I can't remember all
the names. Sorry! If anyone can fill this bit, please do.
Then there was sound check, etc. God, how long did that last? It felt
like an hour, but it was probably only 30-35 minutes."
Thus, if the Wiltern show begins at 8pm, figure Fiona will be on at
least by 9pm. Of course, it's always good to get there early and
reports of David Garza's peformance seem to be positive.
fiona apple forum
I hope this helps. Have fun at the show!