Every type of ecological assessment can be impacted by seasonal constraints and optimum time periods. In terms of an Extended Phase 1 Habitat Survey / Preliminary Ecological Appraisal, it is possible to undertake this form of assessment any time throughout the year. It can, however, be more difficult to identify less common flowering plant species during a Phase 1 Habitat Survey outside of the optimum time of late March and mid-October. That said, it is highly unlikely that your site will have any rare or unusual plants, even if you are working within designated sites or an area registered in England as an area with significant ecological value.