I took my HS education half online half in school, you learn more from the in school stuff, and self- motivation can be difficult.
If you want to do this just so you don't have to go to school, its not worth it, but if its for medical reasons, then you can always try a class or two before starting a completely online program. Also, public school is free, online is not.
As far as at your own pace, you usually have six months to complete a class, but if your a good student and put in two hours per class per day you can finish up five classes in three and a half months.
My personal experiance was you had to put in about 6-8 hours a day give or take ( one to two hours per class) , but you always work at you own level, you dont have to worry about other kids pushing you too fast or holding you back.
P.S. Indiana University High School has an excellent online only program that colleges view as Honors level classes if you do decide that online is right for you. Good luck!