I compare nanoseconds (int):

>>> t=1580301619906185300

# int/int: int.__truediv__(int)
>>> abs(t - int(t/10**9 * 1e9))
172

# int/float: float.__rtruediv__(int)
>>> abs(t - int(t/1e9 * 1e9))
84

# float/int: float.__truediv__(int)
>>> abs(t - int(float(t)/10**9 * 1e9))
84

# float/float: float.__truediv__(float)
>>> abs(t - int(float(t)/1e9 * 1e9))
84

=> int/int is less accurate than float/float for t=1580301619906185300


You compare seconds (float/Fraction):

>>> from fractions import Fraction as F
>>> t=1580301619906185300

# int / int
>>> float(F(t/10**9) * 10**9 - t)
88.5650634765625

# int / float
>>> float(F(t/1e9) * 10**9 - t)
-149.853515625

=> here int/int looks more accurate than int/float


And we get different conclusion :-)