On one hand, thee fear is that if the President announces his run tonight, he'll motivate Democrats to come out tomorrow to vote against his candidates. However, remember that most Democrats that are going to vote already voted early.
On the other hand, President Trump announcing his run will ensure an utterly massive MAGA turnout tomorrow.
Sounds like a good time for Trump to announce he is running.
If MAGA isn’t already turning out, then something’s wrong with them