Laches is based upon the equitable principle that aids the vigilant and not those who slumber on their rights. It is defined as neglect to assert a right or claim which, taken together with the lapse of time and other circumstances, caused prejudice to the adverse party. It is essentially neglect for an unreasonable and unexplained length of time under circumstances permitting diligence, to do what in law, should have been done long ago.
Re T-D Insurance and Zurich 2014 ONSC 3191 discussed laches, including the leading case on laches is In M. (K.) v. M. (H.),  3 S.C.R. 6 (S.C.C.), [M. (K.)], La Forest J. stated, at p. 76, that the doctrine of laches developed because limitation statutes did not apply to equitable claims.
“What is immediately obvious from all of the authorities is that mere delay is insufficient to trigger laches under either of its two branches. Rather, the doctrine considers whether the delay of the plaintiff constitutes acquiescence or results in circumstances that make the prosecution of the action unreasonable. Ultimately, laches must be resolved as a matter of justice as between the parties, as is the case with any equitable doctrine [Italics added].”
36 In that case, La Forest J. held that is was obvious that the defendant had not altered his position because of the plaintiff’s delay, and therefore if laches were to operate, “it must be because of acquiescence, the first branch of the Lindsay rule”: see p. 78. The proposition that acquiescence is a stand-alone branch of laches finds support in R.P. Meagher, W.M.C. Gummow and J.R.F. Lehane, Equity Doctrines & Remedies (Sydney, Butterworths, 2002), at p. 1031:
It is a defence which requires that a defendant can successfully resist an equitable (although not a legal) claim against him if he can demonstrate that the plaintiff, by delaying the institution or prosecution of his case, has either (a) acquiesced in the defendant’s conduct; or (b) caused the defendant to alter his position in reasonable reliance on the plaintiff’s acceptance of the status quo, or otherwise permitted a situation to arise which it would be unjust to disturb.
37 In light of these authorities, I conclude that as a separate branch of laches, acquiescence can, in some circumstances, justify the application of laches in the absence of prejudice.