If you want to set all of your projects to be ready for review on some specific date, in OmniFocus on the Mac, select all of the projects, bring up the inspector, and set the next review date for the whole bunch at once.
Now that I've told you how to do that, let me encourage you not to do so :-)
If you really want to review all of your projects, why not just bring up the project view and look at each project in turn? The only thing that tapping the Mark Reviewed button does is to update the date the project was last reviewed, and the date it will next be due for review. If you are really going to review everything, and you like having different projects on different review cycles, reviewing everything at once (or rather, marking everything reviewed at once) can be counterproductive. For the day-to-day operation of your system (keeping your active projects moving and remaining alert to any impending catastrophes), I think it is better to review every day, looking at a fraction of your projects, so that you give each reviewed project a quality review, rather than an abbreviated glance. As a bonus, intelligent scheduling of reviews means you don't have to set aside such a large block of time—which is easier to carve out of a busy schedule, X uninterrupted hours, or 5 blocks of about X/5 hours? If you divide up all of the projects that are reviewed at a given interval, and set evenly-sized chunks of them to have their next review date today, tomorrow, etc. over the course of that interval, you get a steady stream of work, rather than one big pile. So, take all of the projects you review weekly, divide it in to 7 groups, and set 1/7 to be reviewed today, 1/7 tomorrow, and so on. For a bit of extra cleverness, use a prime number for the review interval, which maximizes the time between cycles lining up.
There are two key things about this workflow: you really want to do some reviewing every day (if you don't, the reviews will get bunched up), and doing any sort of "all projects" review should be done without marking the projects reviewed with the review mechanism (again, you'll undo the optimization). In exchange for that, you get a relatively steady review workload, and you can review individual projects on whatever granularity they require without any changes to your workflow. Got a project that needs daily reviewing, but you do weekly reviews? That's a problem. Got a project that needs daily reviewing, and you do daily reviews? Not a problem. Set the project's review interval to a day. Everything else can stay on a more relaxed schedule.