Howrse~Why when I put my mare to bed, nd I try puttin here in the pasture it says she has to sleep b4 midnight?

I click "Put my mare to bed" and then it says "Where should Ramona sleep?" and I clik "In the box", and then I click "My mare in the pasture" and then it says"How long do you want to put Ramona in the meadows?" Then I select "1 hour 30" and then it says " Warning~You can't do what you asked since your mare has to sleep before midnight!" and I clearly just put her to sleep. Im new and so far i lost 2 horses on 3 different account within 2 days, the first one i aged to fast not noticing the health below 20 % adn the second one I lost becuz i went to my friends for the 2 nights, ans i came back and the health was 16% and i tried like everything to boost its health and i only got it to 18% and the next morning he was dead. My horse now i only aged twice, tht was yesterdey, and i havent aged her since, and her energy is 100% her health is 95% and her morale is 91%. im goin slow on this account. and i ped ridin level 1, and alls i need is a job. but srry for the long story.