The Rosh in Sukka 3:14 discusses the issue of heter b’shaas hadchak as opposed to other times very clearly. K’dai to see.
_________________________
If you take a look at the S”A Orach Chayim, Siman 58, Seif 4, the Mechaber paskens that if an individual who is not an “anoos” went ahead and leined krias shema after alos and before neitz, that person is yoitzeh bediavad.
The MB in seif katan 19 states that if the person who is in a situation of “sha’as hadchak” needs to lein k”s, even on a consistent basis, then it is permitted for him to act accordingly, because what else can he (i.e. no alternative). However, a person who relies of this leniency and is not in a position of “sha’as hadchak” than he may be yoitzeh bdiavad on occasion but if he relies on it consistently, than he is no even yoitzeh bdiavad.