1000 in the timeout almost match "byte time" at 9600 baud /11.0592 Xtal. Also the sender is not obliged to keep the bytes "together" the 232 standard let you send one byte per hour if you so desire.

I have yet to see one program, doing anything significant, that worked flawlessly using polled serial. I advise you to make it your habit to do serial in an interrupt.

Erik