I use to do 3 hour practices on the trumpet the first 2 or so years of my comeback -- now 4+ years in, I am finding that a DECENT HOUR of practice (and sadly, but more important beneficially) - an actual day OFF from playing really helps. Of course, I switch between the trumpet and the trombone in a practice --- so for ME, I am envisioning the trombone is helping also (ie. relaxes the lips between trumpet minutes) -- so my hour of practice is more or less -- a solid hour of playing ((just like GM, ole buddy, ole pal)) -- although my level of play is not quite what ole GM's is. One night or so each week -- I try to play above the staff, do long tones ---- NOT THAT I NEED high range --- but it seems to build endurance, and ability to play, etc.
ps. by the way in community band this week - the guy next to me says - -"gee I ain't got my high C tonight, what do you got tonight" -- so I played (with my mute in) up to the G above High C, pushed no further, and said "gee, you win, all I got is a G"