There is a minor correction in your code. See below
foreach (DataListItem item in DataList1.Items)
{
if (item.ItemType == ListItemType.Item || item.ItemType == ListItemType.AlternatingItem)
{
try
{
Label lbldate = (Label)item.FindControl("lbldate");
string idate = lbldate.Text.Replace("/","-");
string date = TimeAgo(Convert.ToDateTime(idate));
lbldate.Text = date;
HyperLink hreflink = (HyperLink)item.FindControl("hreftitle");
hreflink.NavigateUrl =(hreflink.Text).ToString().Trim().Replace(" ", "-");
}
catch (Exception)
{
}
}
}