I think there is a place on spark where you can enter your goal weight and it will tell you how long it will take to get there based on their recommended calorie range. But if you can't find that then try this link www.freedieting.com/tools/calorie_calculat
to figure out your daily deficit then use this link www.freedieting.com/tools/weight_loss_calc
to figure out your goal date.
For me 1500 calories a day is a little bit less than 1lb a week when I'm sedentary most of the day. But if you have more weight to lose and/or are taller then you'll lose more at the same calorie amount because your deficit would be greater. Assuming about 1lb a week is probably going to be the most realistic goal since it's hard to keep up a 2lb a week calorie deficit without exercise.
It can be difficult to stick to 1500 or less; you have to eat pretty cleanly to do it without feeling hungry....but once you start eating mostly cleanly you may find it is hard to reach 1500 and have to worry about eating enough some days.