Obviously because something went wrong calculating the time, probably because some factor from the S4 run was hardcoded into it. Or because it doesn't take the large number of S4 work in the database into account.
The run is designed to last for something between 6 and 12 months.
BM

Einstein status page - s5 data
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It was completely misleading, because only about 10% of einstein@home users are crunching the S5 workunits. The estimate of finish time will only be accurate when most einstein@home users are crunching S5 workunits. I'll turn the estimation back on in a few days when it's giving sensible predictions. But I thought it was better to give NO prediction than a nonsense prediction.