I would make the following change to you schema. Since # of dogs in a ring can be calculated and you say that end_time is detirmined by the # of dogs. 
create table ring_event (
ring_event_id   integer,
event_name      varchar(20)
ring_id         integer references ring(ring_id),
start_time      time,
time_per_dog    time,
);
-- you can then use 
select a.ring_event_id, a.event_name,
       a.ring_id, a.start_time, 
       ADDTIME(a.start_time, time_per_dog * count(b.dog_id))
         as end_time, count(b.dog_id) as num_dogs
 from ring_event a, tda b
 where a.ring_event_id = b.ring_event_id 
 group by a.ring_event_id;
-- to get the end_time and number of dogs.

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In reply to Re: Interesting scheduling application problem. by gam3
in thread Interesting scheduling application problem. by blue_cowdawg

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