How late is too late?

I hosted my Passover Seder last night — the one I prepped for over a week for and stood cooking for two days straight — only to have the meal delayed and overcooked because I was waiting for  2 guests who showed up an hour late and then forgot the chairs that I needed so we waited another half hour before we sat down.  I was trying to serve early because I had guests who had just flown back from Tennessee and were on central time, and I had 3 kids under 10.  The excuse for being late was that the woman who is pregnant had taken a nap, which I can understand, especially since they hosted the first Seder the night before — but a phone call saying you’re running late with an apology would have been appropriate and appreciated.