Can my employer force me to take block leave in Jul/Aug on short notice?

Started a new corporate job on June 1st. During onboarding, HR mentioned an (unwritten) company rule that everyone takes a 2-week "block leave" in July or August — but HR explicitly told us new joiners are exempt from this for our first year.

I've since finalized 2026 holiday plans with my partner for end of September/beginning of October, which would satisfy the block-leave requirement (2 weeks) and still leave me 4.5 days for the Christmas/New Year period, when we're off anyway.

I'm about to raise this with my manager but I'm worried they'll push back — the block leave rule seems aimed at making sure Jul/Aug is quiet, and business usually ramps up again in September, so they may want me at full capacity then instead.
A few questions:

Can my employer legally override HR's stated exemption and force me into the Jul/Aug window on short notice?

Is there a general rule under Swiss law (OR) about how much notice an employer must give for scheduled vacation, or about employer vs. employee preference when timing conflicts arise?

Since this "rule to take the block leave in Jul/Aug" isn't in my contract or any document I received, does it even have contractual weight?

Any experience with similar block-leave policies, especially as a new hire, would be really helpful.