Hi,
Moderation is best.
There are lots of active or inactive(meditative) exercises within this practice, that allow you to engage in a self practice, doing exercises that compliment your lifestyle on a daily basis.
There are more extreme physical/internal forms of qigong that would be more restrictive to practice, within a 24 hour period of sexual activity. There are all shades of gray too.
If you are basically healthy, you don't really have to be too concerned with this aspect in regards to restrictions. Common sense works here too. Nothing wrong with waiting a short period of time afterwards.
As I said, there is always some aspect of the practice to engage in, regardless of your kidney energy level at the time. Otherwise, someone with weak kidney energy/kidneys couldn't practice qigong, which certainly isn't the case. You will gain a better understanding of this practice over time. There are ways to replenish kidney energy, or feed the kidneys.
The physical aspect of you, that sexual activity involves, is kidney energy. Sort of your battery pack. Although there can be 'specific side effects related to low kidney' energy, the basic "paying attention to self" feeling to gauge this, could be general weakness in doing more physical aspects to your practice.
Meditation, which can be realized as the most powerful aspect to one's qigong practice, is always good, and never restricted, given you aren't in a demanding posture that requires physical strength. Awareness and understanding can be such, that you will be more increasingly aware of these things, and deal with them appropriately, with technique you learn as you progress.
If you 'feel' okay,,, if it feels good to do something within your practice, that is your 'sense' to follow.
You also are storing energy in your practice. You can spend some energy, and still have energy in the bank. Excess, would deplete your funds. 'Saving energy can build a foundation to a higher level practice.' You get to make the choices, and it is always good, better, best, and self compassion. Challenge yourself to progress. Enjoy and live life.
love,
gallen