In general, at least two sessions per week are required for speech, language or feeding therapy. Studies show that more frequent therapy equals more progress faster. In other words more frequent therapy leads to less therapy needed overall.
Part of the reason for this is that less regression occurs between sessions. When a child only receives therapy once a week they forget much of what they learned from week to week. So each progress is much slower.
That said, depending on a family’s ability and willingness to carry over therapy techniques at home this could be and is often adjusted.