I am trying to transfer my data from my old iMac to my new MacBook Pro. I’ve done all the steps and it says it is transferring data between my iMac and my new MacBook but iit is still going after 24 hours.

If you have a LOT of data to move and you're transferring it over Wifi, yes, it can take a long time. This is where a Time Machine backup can be very useful. Moving your data to a new MBP using an external Time Machine drive can be significantly quicker.

<< Does it just take forever over Wi-Fi? >>

yes.

BUT. The default Wi-Fi connection sends data through your 'network neighborhood' to your Router, then back through your 'network neighborhood' to the new Mac.

If both Macs are running High Sierra or later, the procedure says to place them next to each other, and be sure they both have network-names. In most cases, they will create a faster 'Ad Hoc' connection between the two Macs directly, and this can speed up the transfer -- a little. It's still over Wi-Fi, but cuts out the interference and competition from other devices in your 'network neighborhood'.

Using a Time machine backup drive as the source is WAY faster. Rotating Magnetic drives are supported perfectly well over USB-2 at 480 M bit/sec (about 48 M Bytes/sec), which is faster than the steady-state transfer rate of all but a tiny number of Rotating Magnetic drives.