Do you stop eating bread once Seder starts or beginning of the morning of Seder day? Not sure about this
The precise time depends on exactly where you are. For example, the times for Glencoe Illinois for tomorrow are (courtesy of the chabad.org web site)
Finish Eating Chametz before: 10:38 AM
Sell and Burn Chametz before: 11:44 AM
go to the site and change the location to your zip code for relevant times.
From Biblical law, you stop eating bread products at mid-day preceding the seder. Rabbinical law extends the prohibition an extra hour before that to distance from the Biblical prohibition, and a further hour due to the possibility of confusion.