I am wondering if someone can help me out. I am arriving at Terminal 1 at CDG at 12:55pm on September 5. How long do you think it will take for me to clear immigration, customs etc and be outside ready to catch a taxi?

Here's the reason... I am trying to make a 3:55 train at Gare Montparnasse which will take me to Pontorson / Mt. St. Micheal via Rennes

Please let me know what you think? There is a bus that leaves T1 at 2:42 which would get me there within the time for the train. . Any other options besides the taxi from T1 and the bus?

Thanks