About Rematches
You can fight multiple rematches with trainers; however, each time you fight, the trainer's Pokemon become increasingly powerful. Trainers often evolve their Pokemon or catch new Pokemon before the next rematch. Trainers are always located in the same spot where you first met them. The timetable for rematches is based off of the internal clock of your Nintendo DS. If you do not want to wait until Friday for a rematch, temporarily change the date and time on your DS clock from the configuration menu.
Friday Morning Trainers
There are two trainers available for rematches on Friday mornings. The morning is defined as between 4 a.m. and 10 a.m. on "Pokemon HeartGold." School Kid Chad can be found on Route 38 in Johto after you schedule your rematch with him in the morning. He uses a Mr. Mime, Magnemite and later a Magneton at higher levels. Bug Catcher Rob is found on Route 2 in Kanto and always uses Beedrill and Butterfree.
Friday Afternoon Trainers
Three sets of trainers are available for rematches on Friday afternoons, which are defined as 10 a.m. to 8 p.m. in "Pokemon HeartGold." Meet Hiker Parry at Route 45 in Johto for your rematch. He uses Onix and Gravler, then later Steelix and Golem. Ace Trainer Jamie is in Route 26 in Kanto. She always uses Rapidash and either Flaaffy or Ampharos. Young Couple Tim and Sue are found in Route 13 in Kanto. They use Kadabra and Psyduck, then later their evolved forms Alakazam and Golduck.
Friday Evening Trainers
Two trainers are available for rematches at night, which runs from 8 p.m. to 5 a.m. Hiker Anthony is on Route 33 in Johto. He uses Geodude and Machop at first, then evolves them to Graveler and Machoke. He uses three Pokemon in later battles, Graveler, Golem and Machamp. School Kid Billy is found on Route 15 in Kanto. Billy uses three Pokemon to start, Parasect, Poliwhirl and Ditto. Later he adds Mr. Mime to his team and evolves Poliwhirl to Poliwrath.