Although the "Window of Detection" (i.e. the time frame within drugs can be detected in the specimen) differs from drug to drug, the detection windows below can be used as a rule of thumb:
  

Eyes:

Blood:
Oral Fluid:
Saliva:
   
Urine:
Sweat:
Hair:

Impairment - EyeCheck

Hours ("current use")
Hours ("current use")
Hours ("current use")
   
Days ("recent use")
Weeks ("late use")
Months ("historic use")

In oral fluid the detection time for marijuana is 12-24 hours (i.e. "same-day use"), whereas in urine the detection time is normally  a couple of days but can in some cases be up to several weeks. This difference relates to another quality:

Oral Fluid:
Urine:

Contains the parent drug (THC)
Contains drug metabolites (THCCOOH)

An oral fluid test reveals the presence of the pharmacologically active drug in the donor at the time of testing. A urine test relies on metabolites retained in the body's waste system (where they may linger for weeks) and provides no evidence of impairment.

Oral fluid is not saliva, but a combination of what is in the mouth and in the blood. Oral fluid is a mixture of gingival crevicular fluid and saliva and is in fact more akin to an ultra filtrate of plasma and is often referred to as oral mucosal transudate (OMT).

Oral fluid is drawn out of the tissues of the cheek and gums and contains higher levels of antibodies (than common saliva) which closely match those of serum and provides blood-equivalent test results for a number of analysts (alcohol, nicotine, drugs, hormones and infectious diseases).

Sweat and hair testing is not an option at this stage and probably never will be, because of their longer "Window of Detection" which
makes them of little use in regards to workplace testing programs.