What is the best time to apply for a PhD in physics? I am currently an international senior undergraduate physics student, with a 3.41 GPA and no research experience.

I want to apply for PhD program in USA, and I am confused when it is best to apply;
1) before finishing my bachelors degree.
2) waiting to finish it and get engaged in research during my senior year.
3) finish my bachelors degree, get engaged in research, and do a masters degree.

I need to know: does waiting for option 2 and 3 really increase my chances in getting accepted for a PhD program in physics or biophysics? Or should I apply now and save some time?
For a physics PhD in the USA, experience after a four year bachelor's degree is not expected.  However, if you have a three year bachelor's degree or your degree comes from a country with many applicants like China or India, a master's degree may be very helpful.  You should make an application plan no later than the August 1 before you graduate.  This allows time to prepare for the September Physics GRE.  Applying the year following graduation should be a backup plan.