When I enter 1577854800 into an epoch time converter I get Wednesday, 1 January 2020 05:00:00 (which is what I'd expect given your timezone offset for EST ie GMT -5:00).
Can you post the results as returned by your original search i.e.
|eval _time=strptime(Timestamp,"%a %b %d %H:%M:%S %Z %Y")
|bucket _time span=1d
| table Timestamp _time
... View more
What is returned if you run the search
|eval etime=strptime(Timestamp,"%a %b %d %H:%M:%S %Z %Y")
|bucket etime span=1d
| table _time Timestamp etime
... View more