Changing the font size of the time slider pad view is very simple.
You have to edit
/usr/local/etherpad/trunk/etherpad/src/static/css/broadcast.css
find
#padmain {
in the #padmain style section
replace
font-size: 1.2em;
with
font-size: 1.5em;
or whatever font size you want
Save and exit.