From [url=http://www.uesp.net/wiki/Morrowind:Invisibility]http://www.uesp.net/wiki/Morrowind:Invisibility[/url]: You are probably doing something that cancels the spell. Therefore, you either:
1. Need to make sure that you don't do anything that breaks it, or
2. Need to use Chameleon instead, perhaps combining it with Sneaking around, or, of course,
3. Fortify Sneak (get the effect for spellmaking from one of the expansions) and Sneak around.

2 is probably the most effective option here.

Invisibility is generally useful for two things:

1: Sneaking past an enemy that would attack you on sight
2: Getting in a free hit

Sounds like Chameleon is what you're looking for, it basically boosts your sneak skill and is way cheaper that invisibility. Or getting away once you do get caught.

Couldn't you just use a portal spell to teleport away? Or Almsivi/Divine Intervention?

That would do it too.
I just remember using enchanted glass boots of invisibility to sneak around that big floating rock for whatever reason and when they'd see me I'd use invisibility and they'd seem to forget I was there.

Hi

When using invisibility is there a "clock" of sorts letting me know how much time is remaining?

Thanks in Advance and another Thank you to those who have provided answers to my previous questions,

CreamySmooth

Mousing over the Invisibility icon in your effects bar should give you a timer. You may have to be in the inventory menu to do that.