If you have bowel movement and accidentally frontal genital area comes in contact with feces even with wiping properly as femalewould a uti happen in that second or does it take few days to really start? really trying to prevent one from starting?

Forward wiping and contact of the urethra with feces can raise the risk of UTI, but only a little. Any single event like this rarely leads to UTI. If it does, typically UTI symptoms would begin in maybe 2-3 days. There's no certain prevention at this point, but it might be a good ideal to drink lots of fluids to have frequent urination.

In this scenario - no. The body has great defenses to prevent UTI. not all fecal matter may contain infectious organisms. Generally bacteria have to enter inside the urinary opening to cause infection. Infection takes few days to start. Next time this happens wash the area with soap and water. Good luck