It's not currently configurable (certainly something that could be added fairly easily), though it's not hard to tweak in the theme.
From: Bradley Busenius [firstname.lastname@example.org]
Sent: Thursday, March 28, 2013 3:43 PM
To: vufind-tech Tech ý[email@example.com]ý
Subject: [VuFind-Tech] query time
Does anybody know if the query time that shows up in the results can be turned off in the config?