The frequency of meetings with the specialists on a GP committee may vary depending on several factors, including whether both members are equally close to the subject matter, the stage of the research, etc. Sometimes students meet every week with both advisors, sometimes they meet on alternate weeks with each one, and sometimes they meet weekly with one and somewhat less regularly with the other. It should generally be the case, though, that a student writing a GP has a meeting every week or two with some specialist, unless there is some exceptional circumstance (e.g. some writing needs to get done before a meeting will be useful). Difficulty in making progress is generally not a good reason to cancel meetings.
It’s important for students to get feedback on their writing as early in the GP process as possible, and as frequently as possible. When writing is submitted to an advisor, it is a good practice to set an agreed upon time for feedback to be given (e.g. an upcoming meeting), usually within two weeks. If a student doesn’t receive feedback in the expected amount of time, they should follow up with their advisor. If there is any further difficulty in getting feedback, they should consult with the GPD or Head.