STM32F4 Timer accuracy and jitter
PLL is just a frequncy multiplier, output frequency static relative accuracy is just the same as your crystal e.g.
\$3\times (8\,\text{MHZ}+1\,\text{ppm})=8.000008\,\text{MHz} \times 3= 24.000024\,\text{MHz} = 24\,\text{MHz}+1\,\text{ppm}\$. 

Output jitter is depends pretty much on PLL closed-loop bandwidth and power spectral density of timebase oscillator jitter but, long story short, PLL will anyway remove components above its closed-loop bandwidth and hence reduce -or at least do not increase- input jitter