weigh loss

Depends on many variables. But in general, probably within a month, maybe a couple weeks.

What's your starting calorie intake / how much of a deficit will 1200/day give you? The general rule of thumb is that if you cut 500 cal/day, you'll lose 1 lb in 1 week.
Unless you're extremely overweight, don't aim for more than 2 lb lost per week, and unless you're older or very small/short, 1200 cal/day is likely to be nowhere near enough to satisfy.
(Just looked at your profile. For a woman of your age, that might actually work. Have to be careful about how you spend calories.)
If you're used to (for example) 2000/day, start with 1800. Then when you get used to that & start seeing results, go to 1700. Every couple weeks to a month, drop another 100 cal/day. If one step is difficult, hold for a while.


################

Here are some things to read. Definitely read the first several times.

http://community.myfitnesspal.com/en/discussion/1080242/a-guide-to-get-you-started-on-your-path-to-sexypants

http://community.myfitnesspal.com/en/discussion/10012907/logging-accuracy-consistency-and-youre-probably-eating-more-than-you-think

http://community.myfitnesspal.com/en/discussion/819925/the-basics-dont-complicate-it/p1

http://community.myfitnesspal.com/en/discussion/872212/youre-probably-eating-more-than-you-think/p1

http://community.myfitnesspal.com/en/discussion/833026/important-posts-to-read/p1


Goal setting, including weight, calories, and macros
http://www.myfitnesspal.com/blog/MKEgal/view/2014-06-08-setting-goals-667045

Exercise basics
http://www.myfitnesspal.com/blog/MKEgal/view/2014-06-08-exercise-667080

Sleep enough
http://www.myfitnesspal.com/blog/MKEgal/view/2014-08-27-sleep-weight-control-690492

Eating higher protein & lower carbs leads to more weight loss
http://www.myfitnesspal.com/blog/MKEgal/view/2014-08-09-high-protein-diet-685553
Try 45% carbs, 20% fat, 35% protein

Eat about half your calories for breakfast (see the last half of this post for the studies)
http://www.myfitnesspal.com/blog/MKEgal/view/2014-06-10-some-studies-about-weight-loss-667818


Motivation & encouragement (explained in blog post)
http://www.myfitnesspal.com/blog/MKEgal/view/2014-07-24-motivation-encouragement-680938

- Set small intermediate goals & celebrate every one.
- Take measurements.
- Take pictures.
- Weigh yourself regularly.
- Be flexible; forgive yourself.
- Celebrate the non-scale victories (NSV's)
- Don't give up!!!!
- Don't make any food forbidden.
- Eat real food; less processed is better.