swf at night??

I have read alot about it, but my mom really can't do it in the morning due to an early work schedule, and a long drive from the country to the city. Some people have said that it is not good to do it at night? is that true? I know i have always done it in the morning, but thats cause I can... would it be okay if she did a lax tea am & pm instead of the SFW... and then on her days off she can flush?

Thanks.
Happy Fasting
Bhue