You should have a plan, and you should stick to it. But... most importantly you should be flexible, too. I know, I know: you are flexible. Of course you are. But if you happen to come along a bride or groom you suspect could use a little more flexibility, please pass this along to them. ;)
Expect the unexpected
Maybe you spend more time taking pictures than you'd planned because the light is so amaaaazig. Maybe the grand entrance is delayed by fifteen minutes because the maid of honor and best man have, um, gone missing. Maybe everyone got bottle-necked at the buffet table. Maybe Uncle Jimmy's toast went on WAY too long. Maybe all of these and more! You just never know, and you have to be ready to roll with it.
Let it flow, let it flow, let it flow.
Nothing ruins a wedding reception quite like an uneven flow-- like when one thing drags on too long and the next few things feels rushed. Most often, the first half of the reception schedule (dinner, toasts) lingers too long and then everything else (cake, bouquet, garter) has to get packed in before the photographer goes home, leaving very little time for open dancing.
So how to keep the flow going?
Adjust on the fly.
Any delay usually means the next entry on the timeline get pushed back a few minutes and soon enough, you're right on track again. No problem. But even this might require some extra flexibility from certain brides or grooms (no, not you, of course!). In other cases, it means making minor to major adjustments on a moment's notice. For example, it could mean rescheduling your first dance for after dinner instead of before. It could even mean deleting some items from the timeline completely. And how do you know what adjustments to make anyway?
Trust your team.
They do this every weekend, and they're pros at this-- that's why you hired them. So if your day-of coordinator suggests you cut the table-to-table mingling short and get to the toasts, listen to her. If your DJ thinks you should push back the cake cutting and let people get up and dance for a while, it's because he saw half the crowd yawning during your first dance. Remember, you hired these people because they know what they're doing, so let them do what they do best.
Caveat: You do have ultimate veto power, so if something is a deal-breaker, let your DJ and/or coordinator know and they'll work with it.
Just accepting ahead of time that things might not go exactly as planned will probably be enough. It also helps to identify which things you wouldn't mind cutting short if you have to, or eliminate completely-- and communicate that to your team. For example, you might decide that the bouquet and garter tosses aren't something you care about and that, if you're pressed for time, skipping them wouldn't be the end of the world.
So fear not!
You'll be fine, and that's not just me telling you what you want to hear. You really will be fine, and here's why: very simply, it's hard to ruin a wedding. Think about it. You are getting married to the person you love most in the world, you're closest family, friends and loved ones are there to share the moment with you, and they are all supporting you. They want it to go well; they want it to be a wonderful day. Imagine the worst-case scenario: it starts raining and everyone has to crowd inside the clubhouse; the caterers don't show up and you have to order pizzas-- okay, it's not ideal, but wouldn't everyone there just make the best of it and have a beautiful time anyway? Of course, they would-- because they love you, and that's why you invited them. So seriously, fear not. Everything little thing matters on your wedding day but, in a sense, nothing really matters.