Loss of time.

thats a really good sign - and not a bad thing. You are concentrating on the doing part and not worrying about the amount of time being spent.   It sounds like you enjoy polishing a car. If yes I suggest you continue polishing cars as it will be very good for you in th elong run. ( I know this as Meditation By Doing ) .

get a job cleaning cars !

Sounds like zoning out - unless you were locked into thinking about something, and then it would be a thought-loop.

I've had many zoning out moments, sometimes while driving which isn't great - I have driven miles since I was last aware of where I was.  Our subconscious mind can get on with things while our conscious mind takes a break.  Its not specific to autism, its general human thing.

I'm always looking at the time as I like to know what time it is pretty much constantly

I can easily loose track of time when engrossed with something; an activity, perhaps, or often just deep thought on a single concept. But the zoning out your describing, where you kind of 'come to' having been mentally somewhere else, I've mostly had in times of trauma.

i don't think i can explain just how much i relate to this!!

especially transitioning from one task to another- there's always so much dead time. i constantly hate myself for it but i can't exactly control it.

i find in the middle of tasks i completely zone out, even midway conversations. 

i'm still unsure as to how to stop being so frustrated at myself for it though

Oh yes indeed! I've lost many hours even days! Yes seriously days!