Thanks for the comments so far.
Yes, both flights are with LH. It is the early morning LH 983 departure at 0555 from DUB so thats about 1h 40m changeover time in FRA. Given the very early departure I am hoping for an arrival on time and then changeover should be OK.
Of course if we miss it then the probable option is a UA codeshare that day which is not a nice thought.
BTW a very good PE deal from LH, admittedly booked well in advance - significantly cheaper than the alternatives including BA.