How long would it take to 'fix' a terrible sleep cycle?

I'm a college student who doesn't get nearly enough sleep. I regularly go to sleep between 12-1am and wake up at 6am, shattered out of my mind. I'm constantly tired throughout the day and occasionally doze off in class, so this I'm assuming is a sure fire indicator that I'm not really getting enough of the stuff. The blame is probably shared by my god-awful diet.

My question is this; How much sleep does one need/what is the 'optimum' amount of sleep needed to LD regularly? Also, how long would it take to sink into this new sleep schedule/fix my current broken one?

I'd love to commit to LDing properly but at the moment I lack the motivation and I think this is the cause. If you could get me up and running I'd be extremely grateful. :D

P.S. - Does one's diet play a part in regularly LDing and if so, what food/drinkss should be avoided/consumed regularly?

I think between 7-9 hours should be a sufficient amount of sleep, during that time you should be in your 4th or maybe 5th REM stage which by that point in the night your dreams become longer and more vivid. If you can't manage going to sleep earlier to get this sleep maybe you could try napping to make up for lost time, and apparently taking these naps is good for WILDing if you are into that. I don't know how long it might take to get into a new sleeping habit, it seems pretty subjective, but I would guess maybe a week or two.

As far as diet, obviously avoiding caffeine and alcohol helps. And for most people avoiding large meals within a couple hours before sleep is good too. I usually have a light snack before sleep just to avoid being hungry during the night, and it helps me fall asleep easier. Some fruits are good because most have B vitamins that can help with dreaming. And I read somewhere that dairy and high protein snacks before sleep help produce melatonin which helps you fall asleep better.

Hope this helps

There is disputed research that estimates 50% of the missing time needs to be tacked onto a rem state to get back into rythm.

eg: Miss 4 hours of sleep one day? Get back into the goove by sleeping 2 extra hours the next time you sleep.

Of course the problem is sometimes you wake up early... at which point the results become inconsistent.

I'm going to assume you need help fixing your circadian rhythm, so basically I found this "hack" which basically helps you reset it, you can look it up as well if you want to
but I'll give you the idea of it

Pretty much what you do is, don't eat for 12-16 hours I believe BEFORE you WAKE UP
Then once you are awake, eat HEAVY
The next day you will feel sleepy 9-8 hours before wake up time, and at the time you ate, you will automatically wake up at that time.

I honestly forgot why this works, but again, you can look it up if you want to, it did work on me, although it was not right on time, but 10 mins late didnt bother me

I used this when I basically ruined my sleep rhythm during the summer where I absolutely could not sleep before 7AM, the reason for that was I stayed up one night then played basketball at 5AM
for absolutely no reason
I searched a bunch of ways to fix this, and this was one of them it is very helpful, but there are other things that can help such as getting as much sunglight at the day, avoiding light at night
don't do anything beside sleep in your bed, and so forth.