Intraperitoneal use of a drug is similar to intravenous absorption, due to lympathics to the best of my knowledge.

I think peritoneal dialysis absorption rates may give one a good guide to intraperitoneal absorption rates.

It depends on the osmotic pressure across the vessels,that is the intraperitoneal fluid osmotic pressure versus the osmotic pressure in the mesenteric and peritoneal veins. It is also pH dependant.

I would expect it to be slower than intravenous absorption rates. However, you can refer to - "Introduction to Veterinary Pharmokinetics"

Reference:  http://cpharm.vetmed.vt.edu/vm8314/Administration.htm

which states absorption rates are similar to subcutaneous- in Veterinary practice. 

A lot of the animal research published is dated- but the closest on I could find was:

Reference : http://onlinelibrary.wiley.com/doi/10.1113/jphysiol.1951.sp004626/pdf - Figure 5 on Page 343 has just the information you asked for regarding rat Dye absorption-

(Fig. 5. The absorption of dye and of protein from the peritoneal cavity of the rat after the, intraperitoneal injection of 20 ml./kg. of fluid plus 4 mg./kg. of dye. S ,dye; x ---..

protein. Each point represents the average of results on five rats in the case of human, bovine and rat plasma and on four rats in the case of bovine albumin.

The absorption is complete after about 4+ hours in rats -correlating well with the "Introduction to Veterinary Pharmokinetics"

Also-  In general, the rate of absorption is arranged in the order iv ip im sc po (Wolfensohn and Lloyd, 1994).-

Reference: http://www.usp.br/bioterio/Artigos/Procedimentos%20experimentais/Routeadministration-4.pdf