Is it necessary to wait half an hour after urinating before performing Wudu, or is it permissible to perform Wudu immediately in order to catch the congregational prayer, given that drops of urine are known to descend even after this period?

If the urine flow stops, even after half an hour, and the مكلف (person legally responsible) knows that he will find time to pray after it stops and before the prayer's time expires, then he must wait for the urine flow to stop, then perform ablution (وضوء) and pray. This applies even if he misses the congregational prayer, because purity (الطهارة) is a condition for the validity of prayer, unlike the congregational prayer. If he performs ablution and then something (urine) is discharged from him, his ablution becomes invalid.