Muchas gracias por tu ayuda.

Ah my bad, you mean at 1600 as in 4pm and not in 16 from now, so : "for the bus that arrives at 1600 hours". = "para el autobus que llega a las 16 horas/a las 4pm/a las 4 de la tarde" "for the bus that arrives 16 hours from now?" = "para el autobus que llega en 16 horas"

So is it right to say dieciséis horas for 4 o'clock, or is it mil seis cientas horas. If it is the first one, how would I say, "for the bus that arrives 16 hours from now?"

You have to write all that to avoid confusion , or it gets tricky , because a simple correction: " Me gustaría comprar un billete de aquí a Hoyos EN dieciséis horas " can have 2 meanings 1. they understand "for the bus that arrives at 1600 hours". or 2. they understand you want to buy the ticket IN 16 hours, which is silly but it technically is possible. so to avoid confusion: "Me gustaria comprar un boleto de aquí a Hoyos para el autobus que llega en 16 horas"