I would go ahead and file the dispute with the CC company to protect your rights. If the grid arrives later you can always reverse your complaint. If you have any emails from Galaxy stating the changed delivery dates, you should include them in your correspondence with the CC company.

I sincerely doubt Galaxy is stringing you along until the dispute deadline is reached.

Because of their popularity (in large part to all of us who have used them and highly recommend them), they are often backordered on the more popular products. I think they just have not been able to get an order from their supplier yet.

However, if you're worried, then go ahead and contact your CC company - don't just arbitrarily file a dispute - ask the CC company what they recommend and include all the details. Unfortunately, it's the "last minute", so you will need to move quickly on this.