Regarding your questions:
1) This seems quite long. Which OS are you using for your VDI deployment (only Windows 7)?
Not sure on which version of Horizon Cloud/Air your tenant is created, but maybe you have the option to use Instant Clone technology?
If not, when you deploy new desktops a full clone is created, from what I have seen in other regions, the actual cloning part should only take a few minutes. Afterwards, the customization is happening and the Domain Join part. Do you have a DC enrolled near the Desktops in the Cloud? Is sites and Services implemented for the desktop segment in Horizon Cloud/Air?
2) Image Update means refreshing the pool?
If yes, then it is the same as question 1.
Floating desktop pools are refreshed with a new image only when an administration triggers it (Pool Refresh option in /HorizonAdmin).
If a user logs off from a floating desktop, all changes to the desktop are discarded and the desktop reboots in a pristine state again.
When you are doing a pool refresh and a desktop is currently allocated to a user, it waits to refresh the desktop for a certain amount of time until the user is logged off. If the user keeps active or disconnected it could happen that the timeout of the refresh action occurs and you end up with a desktop which is not updated. You should see this within the status of the job in Tasks&Events.