Assalaamu alaikum

Say it and then offer Salam even if this led to delaying your Salam a little.

Many a times during congregational prayer I’m not able to say a prophetic supplication after the durud as the Imam says the Tasleem a little too quickly for my liking. So in this scenario should I say the dua and then end my prayer or should I skip the dua and end my Salah quickly with everyone else? The dua costs me 5 seconds extra.