Summer (June to early October) is the obvious time — the gorge walk is open, the gondola runs, and the surrounding valleys are perfect for hiking. July and August are warm and sunny (Imst sits in a notably dry pocket of the Alps) but rarely uncomfortably hot.
Winter (December to mid-April) brings reliable snow at Hoch-Imst and easy access to the bigger resorts in the Pitztal and Ötztal. The pre-Lenten Schemenlaufen carnival takes place every four years (next: 2028) on the Sunday before Ash Wednesday — an event worth planning a trip around if the year aligns.
Avoid November and May when the gondola is closed for service and most restaurants take their seasonal break.