when i ride on the weekdays i am usually crunched for time...So i usually do around 14-16 miles in about an hour...I was wondering if its ok to go for another ride later that day as well? Maybe a 5-8miler...

It's OK, be careful not to break a nail tho.

I don't see why not. When I am in the mood for both paved and non paved, I ride 20 mi. on my roadie, eat something, then head out for some singletrack on my hardtail.

Just know your own limitations and don't over do it. For example, I would never ride 30 miles road and then head out to a hairy trail with rock gardens and stuff because on the second ride I tend to be more sluggish and cramp prone.

If it is your first time doing 2-a-day, I would suggest cutting the first ride a little shorter and save some for the 2nd ride until you get the hang of it. And make sure to hydrate.

the lengths wont be a problem...i usually do like 30-50 milers on the weekends..i wasnt sure if riding twice a day is bad or not