Letters can be sent any time
Me and my girlfriend are crazy about each other and get along like a house on fire. However, I'm always trying to find more sentimental ways to show her I love her. This is the one she's loved most so far.
I remembered that she mentioned one time how she loved handwritten letters. So, while I was at work, I wrote a love letter to her. It was handwritten and over 4 pages, I told her how much I love her. As our postman comes at about 10am, I was at work when she received the letter. Since most people send letters when they can't see their love, the last thing she was expecting was to get one from someone she saw every day!
I've never seen her smile like when she did when I got home the day she got that letter.