netarc, it doesn't seem that the repeat count is maxed out at 999 nor is it in milliseconds; it's merely a repeat count of each ir string which could vary in length. You probably just typed 999 and figured that was as high as the input box would accept when it actually accepts an enormous amount of digits manually but is truly max'd out at 199 via the up arrow. Give some reasonable numbers i.e. 5, 10 or 15 a try.

Bob's tip is probably more reliable if you can get your timing down right as adding repeats to a full ir string will also repeat the preamble each time.