by the time are adverbs that introduce clauses of relative time. The clause "when I arrive" is called an adverbial clause . It is adverbial because it tells "when" the activity occurs.  Azar (17-2) In linguistic description of temporal location expressions, by the time is a prepositional phrase (PP); that is, by (P) has as its complement -- the time (NP); which has as an adjunct -- a clause. (In current linguistic description, a preposition can be complemented by a wide variety of structures unlike tradtional grammar in which a preposition is complemented by an object.  See Prep Complements ) When denotes a point of time whereas by denotes an interval of time. Swan by:time "not later than" (117.1)  Huddleston CaGEL (8.6.3-4)    Also see When/While . Practice 2 Still Waiting Advanced level Read for errors California has been trying to build a high-speed rail (train) as a clean-energy alternative for travel within the state. As of November, it will be four years since the voters approved a proposition to build the project. The original estimate for building the high-speed rail was around 40 billion. By the time the train is actually built in 2030, the cost will have rose to five times that amount. The system will extend from San Francisco and Sacramento, via the Central Valley, to Los Angeles and San Diego via the Inland Empire. The state expects to complete a 130-mile initial construction segment from Merced to Bakersfield in the Central Valley by 2017. By then, it