One way to do this may be to change the type to a text type in Excel.
Changing this to numeric in Excel is your best option (format as number). Interestingly if you try to do this in Tableau (import normally, change date type from date to number) you run into epoch errors where Tableau's initial date (day 0) and Excel's are misaligned. This adds a day to each duration.
I agree, it's probably neater to fix this in Excel, but just for fun, I wanted to take a stab at doing this in Tableau...
Since Excel is converting to date + time for >24 hours (from 1/1/1900) I feel like you could use that knowledge to back back out to the hours, minutes and seconds in Tableau.
A value in this field of 1/2/1900 10:15:00 AM means that the original data should have had 24+10 hours (34), 15 minutes and 00 seconds. (34:15:00)
So could you make a calculated field to concatenate the DATEDIFF of hours with the DATEPART of the minutes and seconds in Tableau?
+ ':' +
+ ':' +