Sql snapshot in time

I have two tables... One Calendar table One Job table Both have a create date and a client id. I am trying to figure out at the point of someone creating a calendar event for a client at that exact point in time did any jobs against that client exist. If they did exist, was the date the job was added less than 90 days or not. I've attempted doing a join using a datediff between the create dates however what I am struggling with is the order of things. For example if someone adds a calendar event today and then puts a job on tomorrow then that is less than 90 days but actually at the time they created the calendar event e.g. Before the job was added then the job before that may have been greater than 90. Any ideas would be appreciated