It would be helpful to know which miniconverters you are asking about: while most add only minimal delay to the video signal (on the order of microseconds), a unit that incorporates a frame synchronizer like the up/down/cross converter will delay the signal substantially -- on the order of 1/30th of a second for an interlaced format.
For a converter that doesn't synchronize, the delay between input and output will be essentially constant. If you're feeding many typical digital production switchers that have an input timing range of plus or minus half a line of video, the delay added by the converter is almost nil.
On the other hand, a synchronzier circuit will have a varying delay between its input and output -- the exact delay at any moment depends on the relationship between input timing and the reference feeding the synchronizer.
Is your concern video system timing, or something else like minimizing latency in an IMAG system?
Engineering Project Manager
Newport Television, Northeast