Hey experts

I am flying from USA to DUB on Aer Lingus and then DUB to LHR on BA.

Since these were two separate tickets, i built in a 5.5 hour layover in DUB to account for any potential delays.

If all goes smoothly, will BA allow me to standby for one of the several earlier flights once I get to DUB?

Is asking the gate agent my best bet?

Any advice for this inexperienced flyer is much appreciated