A composition for treating a subterranean formation is formed from water, a water-soluble polymer and a crosslinking system. The crosslinking system utilizes 1) primary crosslinking agent of at least one of a dialdehyde benzene source, a dioxane, and a trioxane, 2) a secondary low temperature organic crosslinking agent that generates aldehyde, and 3) a phenol source. The crosslinking system provides the composition a delayed gel time of about 2 to about 20 hours at temperatures of about 250° F. (121° C.) or higher. A method of treating a subterranean formation penetrated by a wellbore is also accomplished by forming a treatment fluid from the composition and introducing the treatment fluid into the formation through the wellbore.