You can put it in a calendar but that is exactly the sort of thing I create a placeholder Omnifocus project for. In fact I actually have one where the project is Birthday Party for R and the action is decide when we will get together for R's Birthday celebration and the time is set to start Oct 1 because R's B-Day is in October. Now I call it a project because I'll likely have to decide what we are doing, am I cooking a special meal, are we going out for dinner, do we want to invite the neighbors etc so I made it a project and when it activates on Monday I'll talk with my hubby and we'll call R and decide what to do.
I don't really have an electronic tickler other than Omnifocus. If it's a single action I just set it up in either my errands list or my misc. single action list in OF with a start date. I use multiple calendars in Apple's iCal system but that is to separate types of work, computer, vs farm vs desk vs in town. My calendar is also my diary of what I worked on as I fill it out at the end of every day with what we actually did.
I nearly always prefer projects to tickler items because I pay attention to projects but ticklers can get forgotten. My OF single action lists are like projects with a multitude of unrelated single items so I deal with them as projects.
When in Projects Section up in the upper left you can select the project filter. If you select Pending you will see all those projects that have start dates in the future. I have several perspectives that I use to filter projects easily. One is all projects, one is on hold projects, one is pending projects and one is active projects.
I have my weekly review set so that when I get to reviewing I do each class of projects separately. When in review mode in OF I use the project filter to first look at all stalled projects. Those are ones that have no next action defined. Often those are projects that i completed or that need some more planning. Then I set the filter as above to be pending projects so I get a sense of what's coming up soon. Then I'll look at on-hold followed by active projects. Occasionally I mix up the order as I find doing them in a different order often refreshes the weekly review and helps me see things I might otherwise miss.
Currently in my system I have the following numbers of the different types of projects:
Active projects: 211
Current projects: 140
Pending projects: 71
On-hold projects: 559
Completed projects: 108
Dropped projects: 25
So I have 71 separate projects with future start dates.
Hope that helps.