There is not a specific time frame for a bereavement letter, but it is recommended that the bereavement letter be both personal and genuine when it is sent, according to The Emily Post Institute. There is also not a set format to follow for a bereavement letter other than to ensure that the writer expresses themselves in a way that lets the recipient know what they are feeling.
It is best to avoid any talk in the letter or note of the specifics of the person's death, such as the way that they died or the types of symptoms that the person had leading up to his or her death. This is often uncomfortable for grieving family and friends, which will make the letter or note painful instead of comforting. Address the bereaved person in the letter and rather than apologizing, express sympathy for the bereaved person's loss.
Most people who write bereaved letters want to know how they can let the bereaved know that they are there to offer support. One of the best ways to do this is for the person writing the letter or note to ask if there is anything that they can do. Some people know that the bereaved has specific needs and may address this. For example, "Please let me know if there is a time that I can bring over a meal for dinner or help watch the kids."