I don’t have a Skybell, so I can’t check this, but if it shows up as a Motion sensor in smartthings, it’s very easy to have motion trigger a light to come on for a specified number of minutes and then go off again using Smart Lights.
If instead, you want to have the light come on when the button is pushed and smartthings recognizes that button as a “button controller” there are three ways to do it.
One) you can use the power allowance option in Smart Lighting, but if you do so, the light will always turn off after that amount of time no matter how you turn it on. That might meet your use case, or it might not.
- see the article in the community – created wiki on how to use smart lighting to create a virtual timer. This uses one virtual switch and three smart lighting automations.
http://thingsthataresmart.wiki/index.php?title=How_to_create_a_virtual_timer_for_a_light
The result should be that when you push the skybell button, the virtual switch comes on. The real light comes on because it is following the virtual switch. The virtual switch turns itself off after X minutes because of the power allowance automation. Then the real light turns itself off because it is following the virtual light.
So this is clunky, but it works. 
- use core. CORE is a very sophisticated community created rules engine. (It calls and individual rule a “piston.”). People in the CORE peer assistance thread can help you with that.
Core has a more complex set up then the method in two) above, but the rule itself will be easier to maintain since there’s probably only going to be one thing to keep track of.
So there you have three different ways to put a light on a virtual timer, depending on exactly what you need. 
Plus the motion sensor option if that is available with skybell. Hopefully one of those will work for you.
( i’m too tired today to pull the full set of screenshots for this, but hopefully it will be clear. If not, someone else can help answer your questions.)