Anything is possible.  It just depends on the size of the model you have or if you already have the motor and electronics (EMC, timer, batteries etc.) Then size the model for the motor size/capabilities.  Lots of sites give the electric motor/glow engines comparable size equivilants.  A timer will work with freeflights and are quite common.  Lots of people use the  small bricks that come in the small/micro rc models such as E-flight etc.  They don't use the RC components, just the EMC, motor, lipo's etc.

Is the Keyway timer available?

http://www.targethobby.com/

awsome prices on parts including mirco indoor electronics.

Here is an updated list on timers. It is not complete.

Brodak

RSM

KP

Atomic

Stevens Aero

They have become much more popular. Most need an ESC unless you run brushless. I recommend that you contact the vender for specifics. I have used the KP unit and was very happy with it. When used with a micro brushed motor it goes in between the motor and battery. That's all there is to it. Adjustable for speed and time. Maybe the size of your thumbnail, probly weighs less.