In my experience the explanations you provide apply more to general flexibility of working hours. Reasonable employers shouldn't have an issue with you stepping

In my experience the explanations you provide apply more to general flexibility of working hours. Reasonable employers shouldn't have an issue with you stepping away from work at anytime as long as your performance is at least adequate. Playing politics might offer a similar result, but I think it'd be easier to lose this privilege if you don't actually have the skills to back it up and are found out. Leaving early for the day is more likely to happen if you complete a big deliverable early than anticipated. Like you reserve a full day for launching a major version, it goes smoothly, so your afternoon is unexpectedly free. The gamble is sometimes you might end up occupied until late into the night, so it tends to balance out.