Nothing in nature happens all at once. They will move south in waves, the strength of the fronts will vary and so will the influx of birds. By late October there should be northern birds in many places throughout Texas.
And not all dove migrate. Some Texas birds never leave home.
Keep an eye out for them. They are a bit larger and darker in color.
Typically they won't stick around for long.
"Count that day lost whose low, descending sun
Is not, in part, obscured by powder from my gun"