The AI Assistant add-on (Chat and Generate combined) shares one daily and one weekly usage budget, shown as "Daily" and "Weekly" bars under Billing on your Profile page. Both chat messages and generations draw from the same budget, there's no separate limit for each.
"AI Assistant requires the AI add-on on an active Plus or Creator subscription"
This means the add-on isn't currently on for your account, either because you haven't turned it on yet, or a pending change to turn it off has already taken effect. See "How do I turn the AI Assistant add-on on or off?" to check its current status and turn it on.
"You've reached your AI usage limit for this period"
You've used your full daily or weekly allowance. The daily bar resets on a rolling 24-hour basis (each request only counts against you for 24 hours), and the weekly bar on a rolling 7-day basis, so it clears gradually rather than all at once on a fixed day. Check the Usage panel under Billing to see exactly how much is used and when it's trending back down.
If you're consistently hitting the weekly limit and need more headroom, Creator's add-on comes with a larger budget than Plus's, see the Pricing page for the current allowance on each.
"Too many AI requests" / "Too many generation requests, try again in N minutes"
This is a different, separate limit from the usage budget above, a short-term cap on how many chat messages or generations can be sent in quick succession, meant to catch a runaway or scripted burst of requests rather than normal, back-and-forth use. It clears on its own, the message tells you exactly how long to wait before trying again. Your usage budget itself isn't affected by seeing this message.