When can one apply for the skilled worker visa when on a graduate visa?

Title - The HR person at work said we would start looking at things later in the year, since the skilled worker visa could only be applied for 3 months before my current (Graduate) visa ends.

I took her at her word cause she's HR and this was back when I was newer at the company but I've just spent some time looking at the skilled worker visa .gov page tonight and I didn't see any mention of restrictions on when to apply, only that the CoS should be issued within 3 months of me applying for the visa, and that was on the switching skilled worker jobs page, not switching into the skilled worker visa page.