Blue? Mine always turned reddish-brown or dark purple if I toned it in 1+9 KRST (for as long as it took). But that might have been Ilford MG FB warmtone. MGIV FB is a fickle beast to tone, heck, it even comes out of some developers looking greenish. Can't have that
Dito the time of 3 minutes for 1+19 KRST to achieve more Dmax.
I normally tone MGIV for 3 minutes at 1:9 dilution. This gives an increase in dmax and a slight shift toward blue in color, but what it really does is neutralized the "greenish" color that most developers give with this paper. I find this a nice neutral combo.
I use KRST 1:9 at 24C. While the toner bath is relatively fresh, MGIV loses green Dektol tint at 1.5m, at 2m DMax starts to improve with no colour shift, and the colour starts shifting around 2.5m becoming visible at 3m as a plum tone in the shadows (not blue). With Ansco 130 MGIV does not seem to have the green tint and the process is subtler, but the timing is similar.
After I transfer the print to HCA toning seems to continue for another 20-30s.