later vs now or never

later

• See you later; goodbye. 

• At some time in the future. 

• Coming afterward in distance (following an antecedent distance as embedded within an adverbial phrase) 

• Coming afterward in time (used with than when comparing with another time). 

• Afterward in time (used with than when comparing with another time). 

• At some unspecified time in the future. 

now or never

• At this sole opportunity, or not at all.