You will arrive in Frankfurt at midday the next day, local time. Frankfurt is one hour ahead of UK time,so your journey will take 15 hours, including the crossing.
If you fancy paying around £145 for a round trip train ticket you can do the journey via Eurostar and TGV in less than half the time, and in much greater comfort. The last time I did the journey it took about 6 hours 20 minutes.
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