You can set the maximum number of posts dlvr.it makes each time it updates your feeds. You just need to set the "Max number of items to post per update period" setting for your feed.

1) Log into your dlvr.it account.

2) Edit your feed

- rollover the feed and click the edit / pencil icon

3) Go to Feed Update Tab

4) Set the "Max number of items to post per update period"

5) Save