what is 1.8 in this expression.
I have seen people using now() + (-1.8) or now() + (1.8) for making 24 hours difference.
What exactly is 1.8
Date and time arithmetic is explained in this help article: https://help.salesforce.com/articleView?id=formula_using_date_datetime.htm&type=5
The value indicates the difference in number of days, hours, and minutes. The quantity to the left of the decimal is the number of days, and the quantity to the right is the fraction of a day.
The value of 1.8 doesn't make any sense for a 24-hour difference, so you need to post more details about your formula and if it actually works.