A 1hr duration means the average value of the measurements over the last 1hr. If you have just configured your alert, and the first measurement recorded is over the limits you set in your alert, the average of the last 1hr is only calculated over this first measurement. An alert will be triggered.
Actions to resolve:
No action needed. The alert will resolve once more data is received, and from then on will only trigger once the average over the last 1hr will exceed your limits again.