I had this issue and created TimeSpan extension class as below.
For usage you just use ToFriendlyString() on the TimeSpan instance.
public static class TimeSpanExtensions
{
    public static string ToFriendlyString(this TimeSpan t)
    {
        return ToFriendlyString(t, Thread.CurrentThread.CurrentCulture);
    }
    public static string ToFriendlyString(this TimeSpan t, CultureInfo cultureInfo)
    {
        if(cultureInfo.IetfLanguageTag.StartsWith("en"))
        {
            return ToFriendlyString_English(t);
        }
        else
        {
            throw new NotSupportedException("This culture is currently not supported.");
        }
    }
    private static string ToFriendlyString_English(TimeSpan t)
    {
        int years = t.Days/365;
        int months = t.Days/30;
        int weeks = t.Days/7;
        if (years > 0) 
        {
            return string.Format("{0} year{1}", years, years > 1 ? "s" : "");
        }
        if (months > 0)
        {
            return string.Format("{0} month{1}", months, months > 1 ? "s" : "");
        }
        if (weeks > 0)
        {
            return string.Format("{0} week{1}", weeks, weeks > 1 ? "s" : "");
        }
        if (t.Days > 0)
        {
            return string.Format("{0} day{1}", t.Days, t.Days > 1 ? "s" : "");
        }
        if (t.Hours > 0)
        {
            return string.Format("{0} hour{1}", t.Hours, t.Hours > 1 ? "s" : "");
        }
        if (t.Minutes > 0)
        {
            return string.Format("{0} minute{1}", t.Minutes, t.Minutes > 1 ? "s" : "");
        }
        if (t.Seconds > 0)
        {
            return string.Format("{0} second{1}", t.Seconds, t.Seconds > 1 ? "s" : "");
        }
        return "now";
    }
}