[kh99]

Ok, you would also need to edit file includes/class_dm_rssfeed.php and find this around line 162, and add the lines in red:

switch ($ttl)
{
	case 518400: // every 144 hours	
	case 345600: // every 96 hours
	case 432000: // every 120 hours
	case 259200: // every 72 hours
	case 172800: // every 48 hours
	case 86400: // every 24 hours
        case 43200: // every 12 hours
	case 36000: // every 10 hours

Apparently when the code was written, someone felt it was important to make sure that value could only be set to one of the "official" values.

I'll look for that other code to see if the fix helps you.