I go to the gym in the early morning but when I worked out over lunch it was:

    00:00 - 00:05 Change into workout clothes
    00:05 - 00:40 Work out
    00:40 - 00:45 Shower (yes a shower only takes 5 minutes if you're not just relaxing under the water)
    00:45 - 00:55 Back into work clothes
    00:55 - 01:00 Back to the desk

Eat at the desk after the lunch break. If that's not practical you can cut the workout in half and have 20 minutes to eat which is rarely not enough time.

If you have a plan and don't waste time an hour is an exceptionally long time.