I'm interested in the "for" part. I know it's common to use half an hour in place of 30 minutes. And I guess I'm talking about verbal expression as a whole, so both spoken and written, although they do differ. Most common, natural-sounding, "good" English speech seems like an oxymoron, and maybe is one, but that's what I'm asking about.
1. I'm going in (to the [noun]) for (half an hour). OR, I'm going in (to the [noun] half an hour).
2. They completed their project for the whole class period. OR, they completed the project the whole class period.
In these examples, the inclusion of "for" seems better in terms of clarity, but I'm sure people using common speech forgo these. Would they be okay to also omit in writing?