Final answer:
There were approximately 900 years between the introduction of Buddhism in Sri Lanka and its arrival at Angkor Wat, with Buddhism reaching Sri Lanka around 2,500 years ago and Angkor Wat beginning its construction in the 12th century.
Step-by-step explanation:
The interval between the arrival of Buddhist influence in Sri Lanka and in Angkor Wat spans approximately 900 years. Buddhism was introduced to Sri Lanka nearly 2,500 years ago by the Sinhalese people from northern India. In contrast, the great temple complex of Angkor Wat in Cambodia, reflecting both Hindu and Buddhist influences, began construction in the twelfth century (1100s CE).