That picture was lame. Here is what I intended on uploading:
{{gwi:1017070}}

shydro
How long are your on/of cycles? As long as they are not extremely long that shouldn't be a problem. Although I would have built it so that the water inlet was on the opposite side than the overflow, that would give better water circulation.

P.S. I have learned that if you drill a small hole at the top of the overflow, it reduces the chances of air bubbles that can do some strange things with rearguards to even filling and draining of the system and/or each individual plant container. Even from unwanted siphoning action in the overflow tube while the pump is running.

Depending on how strong your pump is, and how wide your overflow tube is, that could cause some dripping. But a "T" connector instead of the elbow conector right at the downspout of the overflow tube, with a end-cap or plug in the open end (that has the air hole/s in it) will fix that.

When I was thinking it up, I saw it as ingenious to put the inlet and overflow on the same side for asthetics, less piping and a less cumbersome setup. After I glued it all together and bolted it somewhat permanently to its shelf, it dawned on me that the water might not circulate.

The cycles are only 15 - 30 minutes each. (I just picked up a new timer, so I have two options now!)

Normally I don't like to do cycles longer than 30 for flood and drain systems, although during the summer heat I have done 1 hour cycles during the hot part of the day (I grow outside). 15 to 30 min cycles I don't see any problem with. Although I would always opt for the shorter cycle and just have more cycles if I had that option regardless. As long as it's long enough to flood the system.

Realistically, as long as the system drains without leaving pockets of water in the system, you should not have a problem. The water doesn't really need to circulate when the roots are submerged, and each time the system cycles the water and nutrients mix. You just don't want the roots to be submerged too long no matter what, or they can suffocate. They can suffocate in water that's continuously moving as well.

The water flow from the overflow tube back into the reservoir will still help oxygenate the nutrient solution just the same either way. Because the water drop height (out of the overflow tube) would be the same, and the GPH of the pump is the same as well. Honestly I don't see much of a problem for you other than the more the water circulates, the less algae and other organisms will be able to grow. As long as you already have it glued together, I'd run with it and see how it works.

If you wanted to in the future, it shouldn't take more than 30 minutes to switch it over. All you would need to do is cap the end where the pump is entering the system right now. Then cut the PVC at the other end and splice in a "T" connector for the water inlet. The only hard part is trying to keep it dry as you glue in the new "T" connector. But if it were me, I would just see what happens for now. And as I said earlier, I would use the shorter cycle and just have more of them, that would get better oxygen to the roots anyway (each time it drains it draws down fresh air).

It should work fine.
my EnF I ran this summer was on for, I believe, 8 minutes and then off for about 1.1/2 hours.That'll mostly depend on how well you medium retains moisture.