There is a basic difference between Tisha B'Av and the other Taanios Tzibur. The Rishonim say based on the gemara (Rosh HaShanah 18b) that fast days other than Tisha B'Av were only meant to be kept during the time that there were terrible decrees on Klal Yisroel. During those times the other fasts had the same halachos and stringencies as Tisha B'Av, including starting at night and being forbidden from all the inuyim.
During peaceful times the other fasts are optional. However today it is not optional since Klal Yisroel as a whole has already taken upon themselves to fast the other fasts as well. These fasts however were only accepted in a more lenient way, forbidding only eating and drinking and only starting in the morning. The Mogen Avrohom says (550:3 and Machatzis HaShekel) the reason they were lenient was because it was too hard for the tzibbur. Therefore he says a Baal Nefesh should take on all the inuyim.
The Shaar HaTziyon brings down that today it is also possible to say that we are living in times of decrees on Klal Yisroel, which would require us Min HaDin to keep each fast the same way as Tisha B'Av and even starting it the night before (Shela HaKaddosh see also Mishna Brura 568:9). Therefore says the Piskei Tshuvos (550 fn. 18) a Baal Nefesh should start the fast with all its stringencies, such as not showering, the night before but with regard to not eating everyone may wait until the morning as if it were not a time of decrees.
Important Note: We bring this tshuvah as a starting point for discussion and not to convey any halacha. We try to convey the Tshuva to the best of our ability. We admit that our understanding may not be accurate. One should learn the tshuva to verify the accuracy of our interpretation. Please understand that this Tshuva may not be the final word on this topic. One should consult a Rav before drawing any conclusions.