the official dictionary definition of 'obiad' (and also how we consider it) is 'a hot meal being eaten usually in the middle of a day'. thus we can consider it both as lunch or dinner, depending what time exactly it is eaten (around midday or more in the afternoon, e.g. around 5pm afterwork).
so, as long as it is rather big, hot meal eaten in between the breakfast and supper (or other afternoon/evening tea/snacks) we name it 'obiad'. It is more about the form than the time actually :)
Unfortunately, the end of the sentence doesn't have anything to do here. "Przed" (before, in front of) simply takes Instrumental*. Instrumental endings for masculine singular will mostly have ending -em or similar (see here for more details).
So for example:
before breakfast - przed śniadaniem (neuter)
before lunch - przed obiadem (masculine)
before dinner - przed kolacją (feminine)
*In most cases. To be more precise:
(+ instrumental) before (earlier than in time)
(+ instrumental) in front of (denotes location)
(+ accusative) in front of (denotes movement)
Frankly, I think it's possible to interpret "do obiadu" the way that wladszab wants to, although "together with the lunch" would be my first thought. But I think that especially if we were to turn it into "Do obiadu nie piję kawy", that could be "before". Not sure if it's worth accepting though.