Before I had DS I had 'heard' that TV shouldn't be shown to under 2yos... and when i had DS took absolutely no notice of it at all.
As for time limits, there are none here, DS has watched *at least* 20 mins of TV since he was a tiny baby but this is not a maximum limit at all. His BT hour started with a very gentle programme called Waybuloo which was 20 mins long. Basically he went in the travel cot and watched the TV through the mesh side, whilst I had 20 mins to prepare bottle, bath, pjs and nappy, all his meds etc. There were times I felt people might think I was wrong to do so, but, shrug, it's what I did. I recorded a zillion episodes of that programme so that when they stopped airing it on TV I could show the recordings and our BT routine was intact...and a little sneaky of me, if he needed EBT i could start BT hour whenever I liked with the recording and he totally understood and started to chill out for bed.
Otherwise he has watched TV when he needed to relax after a busty toddler group or a hectic day of playing at the play park etc.
Whilst we have never had time limits and there have been days he's watch lots and lots, there are other days all he watches in that 20 mins before his bath time. Once in a while he might watch a full movie and then ask if he can watch another and I will be more likely to say that I think that's prob enough for now and suggest a few other activities instead.
WRT programmes, mostly Cbeebies, it can be trusted, no adverts and everything is suitable for LOs. Beyond that I am cautious of other programmes and kids movies and those I htink are too grown up I just say he can watch another year when he is older, he loves movies. I personally don't feel that TV need to be all educational for the matter of how does one determine educational? The ability to focus and sustain focus on a task (such as a full length movie) could be considered a skill worth despoiling, the story arc , messages, metaphors etc may also be worth a thought. Being able to discuss after the movie (in simple terms then later more complex) adds to comprehension and can open topics of conversation which might otherwise not have been brought up. Movies or TV shows can also be an "in" to reading because they recognise characters and are interested in those books. octonaughts have a great set of books for instance which have story and facts included.
DS liked most of the Cbeebies stuff, alphablocks, numberjacks, numtums, chuggington... loads.
he was also something of a Youtube addict when he was little for a phase, he couldn't get enough of these train animations, number train, letters train, shapes train, fruit train, colours train... now that I did begin to limit as it was getting crazy, but the TV he mostly self limits.