[manül]

On android channel change without timeshifting is now >20 sec.
With timeshifting 6-7 secs (dvb-t) and 5 secs (dvb-s).

I have serious doubts about the value w/o timeshifting.

The speed difference between dvb-t and dvb-s is noticeable.
During channel change (in both dvb-t and dvb-s) picture is frozen and audio is mute.
When channel is changed (in both dvb-s and dvb-t) picture is perfectly synced with audio.

You can find a good explanation about how MPEG GOP works in noggins post.
I guess your DVB-T device takes longer to warm up than your DVB-S device. On channel switch dvbviewer just sends a channel switch command whereas xbmc/PVR completely terminates the connection and the DVB device will shutdown just to start up a few milliseconds later.

P.S.: Using dvbviewer is all lightning fast (1-2 secs always).

xbmc is a generic player whereas dvbviewer only cares about tv streams. This allows dvbviewer to make a few assumptions about the data which xbmc can not do (e.g. it's always TS/MPEG). Also on channel switch dvbviewer never disconnects from the backend, but xbmc always does. Additional dvbviewer is using RTSP while the PVR is using TS-streams. This might slow down decoding too (never measured).

Tell me what can I try to improve speed in dvb-t, if you want logs, etc..

I don't need and want any logs regarding switching times. But you can go ahead and play with the code. Nobody will stop you.