It would be better for the plants and the fish if you have the period of tank light consistent, not broken into two periods [I'll come back to why momentarily]. As you are not home from 5:30 am to 6 pm (when I was working I had the same hours with the commute) it makes sense to have the tank light on when you are there to enjoy the aquarium. You can set the timer to turn the light on during the day, say 12 noon or 1:00 pm, and off at say 8 pm or 9 pm, depending upon your schedule. There are two things to keep in mind.
The room must not be in darkness when the tank lighting comes on or goes off, so you want ambient room light whether from a window during the day or artificial lighting at night. And this ambient lighting needs to be present for at least half an hour before the tanklighting comes on and at least half an hour after it goes off. This avoids shocking the fish with sudden light/darkness which is not natural. You are aiming to provide a sort of dawn and dusk as in nature.
Second, there must be a period of continuous complete darkness during each 24 hours. This is the period during which the fish's biological processes slow, and the fish relaxes. It is the same as our sleep. So in the example above, this would be from 9 or 10 pm (after the tank lighting and all ambient room lighting is off and the room is in total darkness) until dawn when daylight may enter via a window. The reason for this has to do with the reason you should not have the "daylight" broken up.
Fish, like all animals, have what is called the circadian rhythm, a sort of biological clock that runs on a 24-hour period. Plants have a very similar reactive response to light. The circadian rhythm is governed by light. Not only do the eyes perceive light, but cells do as well; this is why we experience jet lag, and there are problems when daylight savings time occurs. In fish this light/dark is even greater; every cell on their body reacts to light and dark. Once you are regular with the tank lighting, you will quickly observe that the fish will come to "expect" the light coming on and going off. That is because of the circadian rhythm. Experiments with blind fish have proven that this response does not depend upon the fish's eyesight, but because every cell is affected by light and dark.
This is why the period of "daylight" when the tank lighting is on should always be continuous, and roughly the same every day. It makes the fish's life much simpler, as they can save energy for more important things, as there is less stress when everything occurs the same day after day. I know some high-tech planted tank aquarists will suggest the siesta approach, of having the tank lighting on for say 4 hours, off for 3-4, then on for another 4 hours. But biologically this is harmful to the fish. The plants will be affected too, but plants can adjust to varying periods whereas fish cannot, at least if we want them to be in the best health.
If algae is a problem, reducing the "daylight" period is the best way to deal with this, though sometimes an excess of fertilizers can cause algae too. But sort out the light/nutrient balance rather than jumping into something that will be stressful to the fish.
Byron.
im in work 7/8am till 6pm ish. I use a timer which plugs into the mains (light into timer into mains) and have that run between 1pm and 9pm daily 
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