Airlines publish minimum connection times for each airport, the amount of time that should be sufficient for a normal connection. If a connection time is shorter than that, they don't let you book it; and if a connection does meet the MCT, then they accept responsibility for getting you to your destination if delays mean that you miss the connection. The published MCT may vary for international connections (and in some rare cases, for connections between mainline & regional), but otherwise, the MCT doesn't vary by flight.

But should it?

I was looking today for flights from LGA to DFW, leaving as late as possible, and I found this beauty on US/AA:

# 2153
7:00 PM LGA
8:27 PM DCA

# 2218
9:00 PM DCA
11:13 PM DFW

So that's a 33 minute connection, which seems very tight, but this is apparently legal, maybe MCT at PHL DCA is 30 minutes?

But checking the performance of the 1st leg, usairways shows #2153 at 44% on time (within 15 minutes of schedule), 40% late (30+ minutes behind schedule, and 8% canceled.

I guess the other 8% arrived 16-29 minutes late, which would mean a likely missed connection, though at the lower end of that range, with a seat up front on the inbound, no valet check bag to wait on, and a sprint, you might have a small chance.

But even without that 8%, the delay and cancel numbers mean almost half the time, you'll miss the connection. Worse, this is the last flight of the day, so missing the connection means spending the night in DC. Who in their right mind would book this connection - if they notice the short connection time and the performance history?

33 minutes may be reasonable at PHL DCA for inbounds with decent on time performance, or when there are later flights to fall back on. But when neither is the case, I wonder, should US even be selling this connection at all?