Holly, my guy at USC sometimes responds within minutes, I never wait longer than a day. All portal messages are run though nurses first but he always reads them not sanitized versions of them.
The endocrinologist I see never looks at portal messages. Rarely, his nurse will respond. I've found that the ancient art of faxing works better than portal messaging. Some doctors are exceptional. Most are just besieged. AI has already taken over our patient visit summaries.
In the main, your doctor only looks at anything regarding your care minutes before or minutes after they enter the room.