Hi. Ihave been studying for a one and a half year. At the begining I've learned 2-3 hours a day,and I thought I'll speak fluently in one a year. Nowadays I've been studying 4-5 hours, but I have not achived upper intermediate level yet. The truth is that I'm 43 years old and for me is more dfficult learning foreign languages. I know young people who learn just an hour a day,and they speak more better then me. Sorry I think I could not help you:)

i think even 15 mins or more a day is good; as long as you review everything you learnt,  learn a few words and maybe learn some grammar points.