Assuming you are typing in MS Word, try this:
blank document
tools
macros
record new macro
name it whatever
then click on keyboard and okay
Next is customize keyboard panel and you click in press new shortcut key and type Ctrl A or whatever you chose and click on close.
This puts you back in the document recording your keystrokes so you hit Ctrl T, then Ctrl V, backspace twice (to get rid of your tenths you don't need, then hit ctrl left arrow, backspace and type your decimal point (or colon); then hit ctrl left arrow twice, backspace and type your decimal; then hit end to put you at the end of your time then click on stop recording.
I got this from a friend and it works for me. Thanks, S!
Hope this helps, transtype.