As far as I can see the seconds of the periodic trigger is counted from each midnight. As there are 86400 seconds in a day it would be useful with the possibility to add up to a five digit number in the Repeat every Seconds field. There are workarounds, of course, but in my idea it would sometimes be beneficial avoiding hours and minutes all together, so I thought I'd humbly put this out there.
On a slight side note, but not too far off point: While writing the proposition above I realised that it would also be very useful if this input field could be a calculation field, where also variables could be added. This is something I guess would be true for other triggers input fields as well.