The month of May marks the beginning of the cold season in Kruger, South Africa, however, although the temperatures have dipped, your chances of spotting wildlife have upped considerably. The average temperature reaches 20C, which the park's animals find far more comfortable. Rain is unlikely as African winters are mostly dry; the summer months experience rain.
One should be aware of the rules of this park. There are strict rules for visiting hours as well as for visitors spending the night. If you want to spend the night in Kruger, make sure you have your accommodation booked in advance. This is true for the overnight hides as well, including Sable (Sleepover Hide). Spending the night here will offer you the opportunity to potentially spot lions, hippos, elephants, wild dogs and hyenas coming to drink at the nearby water pool. Sirheni is another option, although it doesn't offer overnight camping at all times.
May 31st is a double national holiday for South Africa: in 1910 it became Union, marking the independence from the United Kingdom, and in 1961 it became Republic. This day may have an impact on the park's visiting hours, so keep well informed.