Hi MooMel! More snails ;-)

I almost hesitated to put this as it is pretty close to what the other answers have said. It's just that the term generally used here is 'increasing daylength'. I've put some refs below.

What a shame we are not in that phase of the year now :-/

Numerous animals integrate various cues from the environment to predict the arrivalof improving conditions associated with spring. Arguably the most critical cue ischanging daylength, which is responsible for enhancing numerous behaviors including communicative behaviors. Increasing daylength also fosters marked chemical changesin the brain associated with the behavioral changes.
http://www.epa.gov/endocrine/inventory/NSF-004.html

The number of shoots of the Alstroemeria variety 'Walter Fleming' is influenced by temperature and daylength. In the range of 13° to 25°C the number of shoots increase with the temperature. After a period of 182 days more shoots had been formed at 9°C than at 13° and 17°C. At 13°C the development of shoots stopped nearly completely after 84 days. At 9°C this occurred after 154 days. With different daylengths most shoots were formed at short day, 8 hrs. With increasing daylength, the number of shoots decreased. The percentage of generative shoots decreased when the temperature was raised above 13°C.
http://www.actahort.org/books/51/51_28.htm

Thus, birds wintering in the tropics have evolved a response to that photoperiod which results in premigratory changes similar to that of birds wintering in the North Temperate zone under increasing daylength.
http://www.npwrc.usgs.gov/resource/othrdata/migratio/stimulu...

The relations between the circadian rhythms of melatonin and prolactin, and the effect of melatonin infused into the third ventricle or the mediobasal hypothalamus (MBH) on prolactin secretion and dopamine (DA) release were studied in anestrous ewes under increasing daylength conditions.
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&d...

Ducks are affected by changes in daylength. Increasing daylength encourages egg production while shorter daylength depresses it. Artificial lighting can be used in intensive housing systems to provide a l5 hour constant daylength. This assists in maintaining egg production throughout the year.
http://www.dpi.qld.gov.au/poultry/5378.html

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Note added at 1 day 8 hrs 36 mins (2004-10-12 16:28:46 GMT)
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Hi MooMel

Although I\'m not a big fan of \'translation by Google\', the usage statistics on this term may be of interest:

\"increasing daylight time\" - 0 hits
\"increasing daylight length\" - 5 hits
\"increasing daylight period\" - 1 hit
\"increasing daylength\" - 354 hits

HTH