You will probably have renal dysfunction in about 2 weeks. Kidney damage (namely glomerular lesions) could be found after 4 weeks, I am not sure if earlier you will have renal lesions, because we only tested 4 weeks (2 for diabetes development and the other 2 for pharmacological treatment).

From reviewing the literature it becomes clear that the results regarding almost all parameters / markers of kidney function / kidney injury studied so far are inconsistent within the first 4 weeks post Strepto, thus I would recommend to study rats at a later point in time. 

Ya true, it takes 4-5 weeks. So check your kidney parameter properly before you  use your animals for future studies.

Erdmann Seeliger 

if there is any special scientific  reasons are there for 4 weeks 

usually, hyperglycaemia occurs in 24 hours, and renal complications after 2 weeks, but it depends on whether or not rats are treated with insulin (which can delay glomerular hyper filtration up to 1 month if glycaemia is

the following paper might be helpful:

Tesch GH, Allen TJ: Rodent models of streptozotocin-induced diabetic nephropathy. Nephrology (Carlton ) 12:261-266, 2007

Flavio Sir- Will insulin be not required to keep rats alive for more than four weeks if using a dose of 35mg/kg of STZ along with high fat diet for inducing type 2 diabetes. By STZ administration blood glucose can increase to 400mg/dl and more so how to combat this.