depens on what "overnight" is for you first of all, lets say it 9hrs
1st. Big risk of getting banned, without talking, checking, pauses etc.
2nd. Overnighting is always a big risk becouse you could always get stuck in some random or anything like that.
3. i dont think it possible anyhow, i could manage to do 67-76 in 3 days (lol 4hrs gameplay/day)
jagex are realy slow, it never takes just 1 or 2 days before the ban comes, it took me 11days on one of my accs, then another one i got in 6days, i would say the acc u bot overnight with rune ess .. you could give you last kiss goodbye, dont bot every night, same ammount of hours, doing the same skill, in the same progress..
i can say theirs a 95% chance you cannot do this.
as i use rsbot quite alot, especially fishing.
some figures to help.
to get from 65 to 75 fishing is 760993xp
at 75 fishing on my current rsbot fishing account, i can catch about 600 trout/salmon an hour, power fishing.
to get 760993xp, you will need to catch between 15.2k and 10.8k trout/salmon.
you get 50 xp per trout, and 75xp per salmon. so lets call it 60xp per fish average.
so my hourly rate at 75 fishing is 600x60=36000xp per hour.
and
760993(xp needed for 75 fishing) divided by 36000 (hourly xp rate) = 21
also take into account that i can fish quicker, having a higher fishing level than you currently.
so it would take over 21 hours to get from 65-75 fishing.
i dont think you plan on sleeping for that long.
EDIT: you said 76. not 75, well just look at my calculations and you will see your nowhere near getting 75 overnight, nevermind 76.