Wifes date just does't run for long once off wrist

[Simonas]

I got my wife a second hand datejust from a reputable jewellers last month. She has been wearing it and taking it off about 11 at night and the following morning it is stopping about 4am. 5 hours doesn't seem right at all.

I have contacted the jewellers who have said they will sort it but what is this likely to be as I don't want to keep a watch that is going to be faulty further down the line

Thanks

Simon