Timing bias refers to any issues with the timing of the intervention that could impact the outcomes. For example, in the ALPS study amiodarone was no better than placebo in the treatment of out of hospital cardiac arrest. (Kudenchuk 2016) However, treatment was not given until an average of 19 minutes into the resuscitation, which might be too late for it to have any meaningful effect. Despite being a very well done trial, the conclusion could be wrong if it turns out that giving amiodarone earlier in the resuscitation is helpful.
Timing bias is a type of intervention bias.
Kudenchuk PJ et al. Amiodarone, Lidocaine, or Placeboe in Out-of-Hospital Cardiac Arrest. NEJM 2016.