Apologies if this is entirely the wrong forum. I'll be flying from BWI to MAD in early July.

One of my options is to connect through CDG. If I choose this option, how much time should I allow for the connection? Is one hour too short?

If I connect through BRU, how's 1 hour 25 minutes? Laughably short?

Thanks!

You might consider adding what carriers are involved here. That could make a world of difference in some airports.

It would be United to Brussels, then Brussels Airlines to Madrid.

Thanks!

The 1:25 in BRU would be tight but possible. It is a relatively small and easy to navigate airport. Through CDG I'd allow for 2 hours at a minimum. It is not as convenient to connect through by any means.

Belgium, France, Spain and certain countries in Continental Europe, share a common immigration zone called the Schengan agreement. You clear immigration at the first port of call (BRU or CDG) and there is no need to clear immigration again at MAD.

Whether you have to collect you bags to clear customs is strictly dependant on whether United will inter-line your bags directly to the airline you are flying to MAD with.

So Air France via CDG to MAD should be relatively straight forwards. If you want to fly United, you might have to connect via Spanair which is also part of the Star Alliance so that your bags can be checked straight to.

Not sure if United would inter-line with Brussels Airlines. You need to allow at least 2/3 hours if your bags are not checked through

Yes, they do, assuming it is booked on a single itinerary. UA is pretty bad about interlining bags if not.