Practice Squad players can be signed to standard NFL Contracts (2 yrs $500k) at any time by the teams GM prior to the players 18th game played. [GM's post this as a transaction]
*Even if you just won that player (this rule always applies). As written in the league handbook
http://www.profsl.com/smf/index.php?topic=400603.0 under "PSC".
Practice Squad players can also be called up to the 53man roster
(this is toggle) while remaining under PSC until 18th game played.
They count towards both the 53 man and PS if they are on the active roster under PSC.