osTicket v1.10 (stable) and Maintenance Release v1.9.15 are now available! Go get it now
Thanks to post by Masino Sinaga for version 1.6 osticket, I've followed those instructions and found edits to make on version 1.9.2 to get the Time Spent modification working.
I've not done lots of testing so far, but it does allow for decimal time entry and subtraction (using negative sign like -0.2) for a deduction. I've set my time entry to be on the Post Internal Note tab, but you can move the code accordingly if you want it somewhere else.
See attached notes about altering your database table and editing 3 files. I have not touched reporting at this time.