afni.nimh.nih.gov

Based on what I could find at sites like the link below, I believe those fields are in the format hhmmss.ffffff (hours,minutes,seconds,fractional seconds). The acquisition time would then be at 4:15 PM (16:15 in 24-hr time), 38.3125 seconds.

http://northstar-www.dartmouth.edu/doc/idl/html_6.2/Value_Representations.html#wp1023231