What's the safest way to switch from taking zoloft (sertraline) in the morning to at night?

Not hard: Take the morning zoloft (sertraline) on day 1 as usual. Then wait until evening to take zoloft (sertraline) on day 2. The benefit of an ssri such as zoloft (sertraline) will not "wear off" by the minor delay during the switch, nor would a discontinuation syndrome happen that fast. Taking the first evening dose on the same day as the last morning dose would be more apt to cause a small overdose situation and temporary side-effects.