The standards do not require you do do them all at the same time. Getting DM takes a while, and you can do them one at a time over that time period.
I have never been a really fast surface swimmer, partially because of my body density (major sinker) and partially because I do not do the crawl as efficiently as a more skilled swimmer will--my butt and legs drag, so I am swimming uphill all the time.
The snorkel swim was no problem, so I got a good score on my first attempt. I maxed the tread with no trouble, even though treading is not a sinker's best suit.
That doesn't leave a lot of points to go.
I kept working on my time in the surface swim, and when I got 3 points, I was pretty much there. All I had to do was complete the tow, no matter what the time. I therefore did the tow without any concerns, hauling a buddy into stiff wind and waves off Key Largo. We just estimated the distance. My time was pretty ugly, as you might guess, but it didn't matter.
I could have reversed the last two steps and made my life easier. If I had done the tired diver tow in calm waters (or a pool) with an actual measured distance, I could have gotten a good score easily. Thus, my worst area, the surface swim, would have been a no-pressure lark.
On the other hand, hauling my buddy into those waves taught me an important lesson. That is something that I might conceivably have to do in a rescue scenario, and it is good to be able to do that well.