You are in the right. The whole point of sending flowers is for it to arrive on the right date when you know that person will be there to accept them.
I've sent flowers online before, it worked perfectly - http://www.flora2000.com/
That's the website I used and they did a great job, for future reference. People might have trouble with that company (I haven't read user reviews or anything, double check before you use them) but for me, they did exactly what they were paid to do.