The best time to germinate Plumeria seeds is during the warmer months of the year, typically in late spring through early summer. This timing aligns with their natural growing season in tropical and subtropical climates, providing the following advantages:

1. Optimal Temperature: Plumeria seeds germinate most effectively in warm temperatures, ideally between 75-85°F (24-29°C). The natural warmth of late spring and summer helps maintain these ideal conditions, especially if germinating the seeds outdoors or in a non-climate-controlled setting.
2. Longer Daylight Hours: Longer days during the spring and summer months provide more sunlight, which is beneficial for the young seedlings once they emerge. Adequate light is crucial for the healthy growth of Plumeria plants.
3. Easier Transition to Outdoor Growing: If you start the seeds indoors, the warmer months make it easier to transition the young plants outside as they will be less likely to experience shock from cold temperatures.
4. Extended Growing Season: Starting seeds in late spring or early summer gives the seedlings a longer growing season to establish themselves before the cooler weather sets in.

However, if you are germinating seeds indoors in a controlled environment where you can maintain consistent temperature and lighting, you can technically start them at any time of the year. This flexibility allows for year-round propagation, which is especially beneficial for gardeners in cooler climates or those who grow Plumeria as indoor plants.