I don't take Sertraline but another drug of the same class (Citalopram and I take it in the morning). Some of the other classes of anti-D's should be taken at night (the tri-cyclics), but the patient info with Sertraline says as long as it's taken at the same time each day, either morning or night.
It's probably something to bring up with your doc. I wonder if it's your disease making you tired by lunchtime rather than the drug? I know that's true for many of us.
Maybe someone else will come along who is on Sertraline (Zoloft) with their personal input.
Are you also on Tramadol? The patient leaflet says it's best not taken with Sertraline, there must be other similar drugs though that are ok with Tramadol.