Chasidut su Salmi 19:6

One should take care to pray, whether in summer or in winter, before the rising of the sun. That is, the majority of the prayer, almost up to the recitation of the Shema, before the sun rises. For the distance between before and after sunrise is as the distance between East and West, since before it rises one can still easily nullify the forces of harshness. This can be seen in the verse (Psalms 19:6) "And he (the sun) is like a groom going forth from his canopy, eager as a hero, etc... and nothing is hidden from his heat (michamato)." Don't read this word as michamato, but rather micheimato, "from his anger!" This means that once the sun has gone out over the land, then nothing is hidden from the forces of harshness that derive from the fiery angels of the sun. This matter, therefore, should not be seen as insignificant in your eyes, for it is a great matter. The Baal Shem Tov, may his memory be a blessing, would be very particular about this, and occasionally he would rather pray at this time alone, if a minyan could not be gathered.