Excel IF function with Datedif function nested is not working

I have an excel spreadsheet and I am trying to make a column that calculates the difference of days between 2 dates. If the difference is less than or equal to 45 days the 0.5 is added to that column. If it is greater than 45 days then nothing is added. I cannot figure out why it won't accept my function I have made

=IF(DATEDIF 'Jira Sheet'!$I2,'Jira Sheet'!$J2,"D") < =45, + 0.5,+  0)