We only moved over to Blesta in April as soon as v4.0 was released and we put this on PHP7. We've had no issues so far, all seems to be working very well and worth the switch from an old version fo WHMCS we used to use.
It usually takes a short amount of time (unless they have automated the process some more) as they watermark the images for you. I have usually had a 1 day or less turnaround time.