Fix division by zero
Fix division by zero

time.time() has single decimal precision on some Windows versions (Appveyor).

FrancescAlted/PyTables,PyTables/PyTables,FrancescAlted/PyTables,avalentino/PyTables,FrancescAlted/PyTables,avalentino/PyTables,PyTables/PyTables,PyTables/PyTables,avalentino/PyTables