As a beginner, Sentence Mode is definitely useful, I agree. If it’s material created or shared by LingQ, you can ask them to fix the timestamps and they usually will, when they have time. If it’s material shared by volunteers, then it’s unlikely it will get fixed, because manual timestamping is very, very time-consuming and we are volunteers after all. 
If timestamping is important to you, I suggest you start with material created and shared by LingQ, such as the Mini Stories. Another source of usually correct timestamped material is to import your own lessons. If you have clearly spoken audio with no music or what not in the background and perfectly matching text, the ‘Generate Timestamps’ function works quite well, at least in some languages. Another source is to use the LingQ Importer browser extension to import videos from YouTube. Subtitles must be timestamped, so the LingQ Importer uses these timestamps and they are usually great.