I am typically gone for about 10 hours during the weekdays. Is it safe to leave the food on the warm setting for the remaining 4 hours before I get home or should I stick with recipes that have a cook time of 8-10 hours?

You can check if it is safe to use a delayed start technique with your pot. Assemble the dish the night before in the crock and put in the fridge overnight. Check temp in the middle of the dish, write it down, and then put in the crockpot on 2 hour delay (this is the MAX delay you should ever use). TEMP SHOULD BE 40 or less.
Check at 1 hour, write down, it is not cooking. Record temp.
At 2 hours when it is just getting to start, check temp and write down. This temp will probably be between 40 and 100.
1 hour later, check temp and write it down. TEMP SHOULD BE over 160.
1 hour and 20 minutes later, check temp and write it down. TEMP SHOULD BE over 180.
At end of cook cycle, check temp and write it down. TEMP SHOULD BE over 180.
2 hours into warming cycle check temp and write down. TEMP SHOULD BE over 170.
Check before you eat. Temp should still be over 170.

If the temp after 1 hour of cooking is lower than 160, you should not use the delay start technique with you pot, it doesn't heat fast enough.

You can slow down a recipe by cooking more at the same time, freeze the rest. You can also put in some whole potatoes or other chunky veggies, these cook slower than meat and will extend the cooking time.