Hi,
It depends on your requirement and the need for specific application that may require a longer time out window.
The config guide does not mention anything about needing to reboot the devices.
from the config guide:
Step 4 
To set connection timeouts, enter the following command:
hostname(config-pmap-c)# set connection timeout {[embryonic hh:mm:ss] {idle hh:mm:ss [reset]] [half-closed hh:mm:ss] [dcd hh:mm:ss [max_retries]]}
where the embryonic hh:mm:ss keyword sets the timeout period until a TCP embryonic (half-open) connection is closed, between 0:0:5 and 1193:00:00. The default is 0:0:30. You can also set this value to 0, which means the connection never times out.
The idle hh:mm:ss keyword sets the idle timeout for all protocols between 0:5:0 and 1193:00:00. The default is 1:0:0. You can also set this value to 0, which means the connection never times out. For TCP traffic, the reset keyword sends a reset to TCP endpoints when the connection times out.
http://www.cisco.com/en/US/docs/security/asa/asa82/configuration/guide/conns_connlimits.html
HTH
