The reason you are coming up short...
You also need to make similar calculation for heating the glass cup.
The sum (time to heat water + time to heat glass)
is the time it takes to raise the temperature 85 deg
glass cup, mass= 300g (given)
You should have a table in your text of specific heats for other materials or ask your teacher.
One online source gives specific heat of glass
= 0.84 J/(gm/deg K).