The word of the day is hysteresis:
< Greek ὑστέρησις a coming short, deficiency, < ὑστερεῖν to be behind, come late, etc., < ὕστερος late.
A phenomenon observed in some physical systems, by which changes in a
property (e.g. magnetization, or length) lag behind changes in an agent
on which they depend (e.g. magnetizing force, or stress), so that the
value of the former at any moment depends on the manner of the previous
variation of the latter (e.g. whether it was increasing or decreasing in
value); any dependence of the value of a property on the past history
of the system to which it pertains. (OED)
"Lag time will depend on the system being studied. A lag of 30 sec, or longer, may not be a problem in some assays if a long linear region is then observed. If the primary enzyme is suspected of being hysteretic, the lag time should be minimal to ensure the actual measurement of the primary enzyme's behavior."
- "Techniques in Coupled Enzyme Assays", Rudolph et al., Methods in Enzymology, 63:22 (1979)