Timed feeders work well for giving your cat food when you are away at work. There are even ones that have a microchip reader, so if there is more than one cat in your home, you can program the feeder to only let the cat with the correct microchip eat.
Frozen cat food "hockey pucks." Take some of the canned food, put it in small portions on a cookie sheet and freeze in your freezer. Bag the frozen "hockey pucks" in a ziploc bag for later use. Take out 1 or 2 and leave out to thaw while you are away.
Could you be more specific on what those kibble foods are? I know of no dry food from Hill's or Royal Canin that are low enough in carbs for a diabetic cat to eat. RC Glycobalance? Hill's W/d or M/d? Something else?
Check this list, to see if the canned foods you are feeding are on it. Then, you need to see if the Carb % is <=10% carbs, which is more appropriate for a diabetic cat.
Cat Food - Nutritional Composition, data compiled by Dr. Lisa Pierson, DVM (2017)
How much to feed depends on if your cat is gaining, losing or maintaining weight each week. Weigh him at home, and track it on your SS, over in the Remarks column on the right hand side of the spreadsheet.
Hold cat in your arms, step on a human scale, note weight, let cat down, note your weight, subtract 2nd number from first number to get cat's weight.