If you want to collect goshuin at Shoren-in Monzeki Temple, I would personally recommend visiting during the day. During special nighttime viewings, the goshuin available at the temple office are more likely to be prewritten. If you want one written for you on the spot, you have a better chance during the day.
The nighttime illumination is certainly beautiful, and the garden and buildings take on a very quiet, mysterious atmosphere under the dim lighting. However, the drawback is also obvious: many of the architectural details are difficult to see. If your main purpose is to appreciate Shoren-in itself, including its temple buildings, painted sliding panels, and gardens, I would actually recommend visiting during the day.
In addition to Kachoden Hall, Kogosho, the Main Hall, and Shinden Hall, Shoren-in’s grounds include a strolling pond garden centered on Ryujin Pond, traditionally said to have been designed by Soami. There is also the Kirishima Garden, which is traditionally associated with Kobori Enshu. These are all better appreciated slowly during the day, especially the details of the gardens, the proportions of the buildings, and the borrowed scenery, much of which is lost under the nighttime lighting.
Special nighttime viewings also usually cost a little more than regular daytime admission, so unless you are visiting specifically for the illumination, I personally think the overall value is better during the day. Of course, if you really enjoy the quiet and slightly mysterious atmosphere of temples at night, Shoren-in’s illumination is still worth experiencing once.
At the time, I did not have enough photography experience, and looking back now, I feel like I did not make the most of the illumination that evening. Shoren-in’s nighttime lighting is dim to begin with. In many areas, instead of lighting up an entire building, it uses localized lighting to create atmosphere. So if you want to take photos, it is best to prepare a camera or phone with good low-light capabilities. If there is not even much moonlight that day, the demands on your equipment and your ability to hold it steady will be even greater.