So in Volume 2 of the NGNL LN and Episode 6, we see Jibril react to a nuclear bomb. However, in the novel, it is specifically suggested that she moved to touch the center of the table's crystal after the secondary explosion had occurred. This process should occur in microseconds, if not less. Some proof to that claim:
Claims that after a secondary explosion chain reaction starts, the explosion occurs in a few microseconds
The picture in the article suggests that it takes 10^-7 seconds for the explosion to occur from detonation - this includes the secondary explosion, so it is a magnitude higher than the last article.
This reddit comment says that it actually takes hundreds of nanoseconds for the entire process - which is in line with number two
4. https://www.quora.com/How-long-does-a-nuclear-explosion-take
This Q and A also suggests a reaction on the scale of nanoseconds, although that might be hundreds of nanoseconds as well.
Keep in mind that Jibril had to both outspeed this time interval and vocalize her spell to protect Shiro/Sora before it detonated, otherwise they would have been turned to mush.
So my low-end will be 3 microseconds (source #1) and my high-end will be 0.3 microseconds = 300 nanoseconds (source #2, 3, 4 ).
I'll employ pixel scaling to get how far she traveled.
We'll assume that Sora's head = the average head height of a man = 0.218m
Sora's Head = 0.218 m = 50 pixels
Jibril Chair-Crystal = 200 pixels = 0.872m

Low-end: 0.872m/(3x10^-6s)= 290666.67m/s = Mach 847.42
High-End: 0.872m/(1x10^-7s)= 8720000m/s = Mach 8474.2
One hell of a range I suppose. But I already calc'ed Jibril earlier at being Massively Hypersonic+ and some of this calc is a lowball so it can be considered either a bit feat or proof of some extra reaction speed.