Transfer speed question

so a build Im getting boasts that the read/write speed is so fast load times are almost nonexistent. However the drawback is the storage capacity is low and the files sizes are huge. So in order to have space you have to keep the files on a USB external drive then transfer to the super fast low capacity internal everytime you wanna use it, then tranfer from internal back to external when done thus making the "no load times and no more waiting" claims broken since you have to tranfer files to and from storage to get that speed

So my question is this. How long would it take to transfer a 100gb file from a regular USB 3.0 5400 ram hard drive to a "super fast" internal SSD. Then how long to tranfer back from super fast SSD to usb external?

I would think the SSD drives speed wouldn't matter at all cause it would be limited to whatever usb 3.0s transfer rate is right? But yeah timewise roughly how long would both those transfers take?

And does the speed change when transfers g from the USB 3.0 to the internal SDD and or transferring from the internal SDD to the USB 3.0 drive?

So then translating that into minutes (and using the ACTUAL transfer speed and not the on paper/advertised transfer speed of USB 3.0) how long would a 100gb transfer take