Yes, there are certain mail delivery times. Here is the schedule for the V4. (The V4.5 is probably the same.)
?:?1 AM (1 minute after morning wakeup) - star
9:30 AM - letter
10:30 AM - letter
11:30 AM - letter
12:30 PM - letter
1:00 PM - star
1:30 PM - letter
2:30 PM - letter
3:30 PM - letter
4:00 PM - star
4:30 PM - letter
5:30 PM - letter
The number of regular letter mail you receive per day is random. Some days you may receive 5 or 6, other days only 1. Delivery times are 30 minutes after the hour, from 9:30 AM to 5:30 PM (perhaps as late as 6:30 PM). (Meaning, 9:30 AM, 10:30 AM, 11:30 AM, etc.) You may not get mail at those times, but if you get mail it will be at one of those times.
Special delivery [!] - times depend on your life cycle of your tama character, such as the time you hatched it, and how long it was paused.
