Understanding an assumption about setup times in ion implantation

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I have a question about a statement in Mason & Fowler's 2000 paper, Maximizing Delivery Performance in Semiconductor Wafer Fabrication Facilities, about setup times in ion implantation.

Finally, in order to create a more realistic set of data for our analysis, the sequence-independent setup times associated with the medium- and high-current implanters in Dataset 1 were replaced with sequence-dependent setup times (Table 1). Specifically, if there is any change in the tool's required dopant species, 30 minutes of setup time is required. An additional 30 minutes is required to change from phosphorus (P) or arsenic (As) to boron (B) or boron difluoride (BF2). Finally, changing the wafer's tilt angle requires 15 minutes. BF2 and As steps have a tilt angle of 0 degrees, while B and P steps required 7 degrees of tilt.

Is this a reasonable set of assumptions? What takes so long to switch dopants or tilt angles? And why does the tilt angle need to change?

(I know very little about ion implantation, just trying to get a sense of how stuff like this works)