Ok, OP, if you have 1 fl. oz. that only contains 60mg(appx. 1 grain) of codeine, and about 35mg of promethazine. Given you have the standard phenameth w/codeine Rx, that is.
First off, 1 measly grain of codeine aint gonna do jack shit unless you're more opiate niave than a baby born to a mother who didn't even get a pinch of Demerol when giving birth LOL.
Secondly, lets assume you and your 3 friends "SIP THIS LEAN like lil wayne cuz he sooo cool!! omg!", lets assume you sip your shit right? Ok well that's your first mistake. And that will waste your measly amount of cough syrup.
Seeing as you only have 1 oz. per person everybody's just gonna need to take theirs in one shot. If they want any sort of "high" at all..which they won't get because you don't have enuff...even if they did this stuff is hardly recreational.
I just got myself an

z bottle 3 days ago.
I dose my shit as follows; 4oz. the first day, 4oz and a 20mg Adderall the second (because all that Goddamn Phenergan makes me tired as fuck).
I was really only drinking this stuff because I burned through my norcos and can't find shit right now, not even a bail of hay. So this stuff kept me alright for those 2 days.
P.S. i'm pretty sure i'm allergic to some ingredient in this because when I drink 2+ oz's consecutively (usually drink all 4 within 15 mins), I get chest tightness and pain which goes away as soon as the codeine kicks in. It can be pretty excruciating though so watch out for that, if you do get it, don't worry too much, just smoke some weed and wait 20 mins and it will dissipate.
P.S.S. I'm pretty sure it's the alcohol in the syrup because I get the same chest pain when I drink certain types of clear liquor.
OH and as for the "will we be straight by 10pm" question, idk if you mean will we be high by then or will we be sober by then lol..for me its high. Assuming you have to talk to your parents or some shit lol don't worry they will have no idea because you gonna do such a small amount.
You might not even know you've taken anything lol. But be careful bro. And really, if your gonna abuse opiates, get something pure, like oxy. It's a lot safer than consuming a bottle worth of promethazine just to get well or whatever reason youre drinking this crappy stuff lol.
Codiclear-Dh FTW!!! Fuck that tussionex extended release bullshit.