is it ok to clean my bearing even though my yoyo is made of celcon? will it e bad if i leave the shields off after i clean it?
the answer is yes, it will not affect your plastic even if it is deshielded,just make sure you spin it on the tip of a pencil to get the mineral spirits off. 
this will most likely increase my spin time right?
Yes - Unless the bearing is very well broken in already. If it is broken in, then spin time might be less.
How long does your bearing spin when you flick it?
about 3 seconds
Then cleaning it would be an Improvement