The answer to 'best time for retaining wall installation' is that the best time is typically in the spring or fall. During these seasons, the weather is mild and the ground is not frozen, making it easier to excavate and install the retaining wall. The cooler temperatures also allow the concrete or mortar to cure properly without drying out too quickly.
Installing a retaining wall in the summer can be challenging due to the hot and dry conditions, which can cause the concrete or mortar to cure too quickly and potentially lead to cracks or other issues. Similarly, winter installations can be difficult due to the frozen ground and the risk of the wall being damaged by frost heave or other cold-weather factors.