Practice is the absolute key
In my view, you are practising too much when
- you are not enjoying it anymore
- you are not noticing any improvement between sessions
It sounds to me like those things are not happening, so I say carry on!
I too am on the dang thing nearly every spare moment, and I can create spare moments by neglecting; housework, yard work, ironing, entertaining, going out, visiting, watching TV. But hey I am enjoying doing what I am doing....so yep if I'm enjoying it I'll continue banging away.
As for whether I can discerne improvement on a day to day basis, not so sure....I do have
days when I'll be banging out the same song, slowly or fast, over and over again, but again I enjoy it so I dont feel I need a break just cos I'm not noticing any improvement, but it is improving, keeping tempo better at least and strumming better.
I'm surprised I haven't given up really!! The further down the track I go the more I see what talent others have and feel I'll never be on par....but somehow it doesnt matter to me, I'm just having fun and enjoying the trip I'm on....where It leads to is immaterial to me at this stage....I dont have an expectation of what degree my proficiency should be...I just know that I am a better ukulele player than any of my friends, lol.
In summary, if you're enjoying it, strum away!!!!!