After changing from 16 to 24 bit I discovered that midi tracks speeded up.
This is what I tried out:
I recorded 6 miditracks: 2 tracks vst, 4 tracks keyboards.
By recording these tracks the project setup was set on 16bit/44.1khz
After 16bit midi recording I wanted to try out audio-recording in 24bit.
Didn’'t work because the speed of the midi track changed.
Is it possible to change tempo of the midi events and also change the sustain and other midi-effects?
Thanks for your suggestions! 
I think you may be getting confused a bit (pun intended)
The bit depth will not affect the project play speed/tempo/pitch, and various bit depths can be used in the same project without problem.
The sample rate will affect the project and should be decided on at the start, once set any change will affect the project play speed and pitch and should not be changed.
Also, MIDI data is unaffected by bit depth settings as it has nothing to do with incoming audio, so any VSTi’s you may be playing from a MIDI track will be totally unaffected. The main influence of the bit depth setting is on recorded audio, whilst recording via an audio interface. It will also have an influence on some other processes, but only ones that result with files actually being written to disk.
Again THANKS for your answer 