df(mm) minutes padding zero is lost when as (if) output combined with text "" +
$if(1, df(mm, ci(start, 0)))$
00 << works fine as output of 'if'
$if(1, "" + df(mm, ci(start, 0)))$
0 << add additional text, it drops zero padding
$if(1, "" + df(mma, ci(start, 0)))$
00PM << add AM/PM and it works again
* For simplicity, I did remove the proper 'if' condition and "text" between quotes, but it's the same;