A transfer initiated at four in the afternoon on a Thursday and one initiated at nine on a Friday morning can land on the same day, at different rates. The reason is cut-offs, not speed.
Cut-offs
Each provider has a time after which the transfer is processed in the next cycle. Sending after it does not make the transfer slow; it makes it tomorrow's transfer, at tomorrow's rate.
Weekends and holidays
Markets are closed, so the rate applied is usually a held rate with a wider spread to cover the risk of holding it. That is why weekend transfers quietly cost more even when no fee changed.
If the transfer is not urgent, initiating on a weekday morning rather than a Friday evening is the single cheapest habit on this whole site, and it costs nothing to adopt.
What timing does not fix
The spread and the receiving charge do not move with the clock. Timing shifts a few per cent of the cost, not the structure of it.