SELECT `User_id`, time(sum(`Date_time`*(1-2*`in_out`)))
FROM `whatever_table` GROUP BY `User_id`;
The (1-2*`in_out`) term gives every login event a -1 factor and every logout event a +1 factor. The sum
function takes the sum of the Date_time
column, and GROUP BY `User_id` makes that the sum for each different user is created.