I am wondering how this number was obtained?
if you want 1.65 to show as 2:05.
based on the other comments the 1 represents an hour - if that is the case then how did the digits to the right of the decimal ever get above 60? I am suspicious of that.
Anyways, just to parse the text you could use(value is in A1):
=IF(RIGHT(A1,LEN(A1)-FIND(".",A1))>60,LEFT(A1,FIND(".",A1)-1)+1,LEFT(A1,FIND(".",A1)-1))&":"&IF(IF(RIGHT(A1,LEN(A1)-FIND(".",A1))>60,RIGHT(A1,LEN(A1)-FIND(".",A1))-60,RIGHT(A1,LEN(A1)-FIND(".",A1)))<10,"0"&IF(RIGHT(A1,LEN(A1)-FIND(".",A1))>60,RIGHT(A1,LEN(A1)-FIND(".",A1))-60,RIGHT(A1,LEN(A1)-FIND(".",A1))),IF(RIGHT(A1,LEN(A1)-FIND(".",A1))>60,RIGHT(A1,LEN(A1)-FIND(".",A1))-60,RIGHT(A1,LEN(A1)-FIND(".",A1))))