Length of dispersal flight of European spruce bark beetle?
The number of days may still be unknown, and it is probably a large variation when they find a suitable host tree. The "pioneer males" might use "random-walks", when they try several trees before they chose the right one. Its also a large difference between endemic and epidemic periods regarding dispersals. 

Anyhow, the flight distance of I.t. has been shown to be more than 8 km (see Botterweg, 1982), but during outbreaks when it can be pheromone sources everywhere most of them may disperse less than 500 m and maybe even less than 100 m. See: 

Kautz. 2011. Quantifying spatio-temporal dispersion of bark beetle infestations in epidemic and non-epidemic conditions. 

Whichmann and Ravn. 2001. The spread of Ips typographus (L.) (Coleoptera, Scolytidae) attacks following heavy windthrow in Denmark, analysed using GIS 

and as mentioned above, the dissertation by Kärvemo and articles within. 

I hope this helps.

cheers

Simon