http://www.aaib.gov.uk/cms_resources...Appendices.pdf
1 GENERAL 1.1 Wording
The emergency procedures describe the actions the pilot must perform according to the various cases of failure. However, according to the high diversity of the outside factors and type of terrain overflown, the pilot may have to adapt to the conditions from his experience. To help the pilot in his decision, the following four expressions are used:
LAND OR DITCH IMMEDIATELY
Self-explanatory.
LAND AS SOON AS POSSIBLE
Emergency conditions, land at the nearest site where a safe landing is possible.
LIMIT DURATION OF FLIGHT
Land at the nearest site at which technical assistance may be expected. Extended flight is not recommended. Duration of flight is left to the pilot’s discretion taking into account the operational environment.
CONTINUE THE FLIGHT
Self-explanatory.
LAND / DITCH IMMEDIATELY
The consequences of continued flight are likely to be more hazardous than, for example, ditching or landing in trees. Where the instruction "Land or ditch immediately" is given in a checklist, the procedure for 'emergency landing' should be followed.
On the other side of the coin/pond
http://www.robinsonheli.com/manuals/.../r22_poh_3.pdf
Land Immediately - Land on the nearest clear area where a safe normal landing can be performed. Be prepared to enter autorotation during approach, if required.
Land as soon as practical - Landing site is at pilot’s discretion based on nature of problem and available landing areas. Flight beyond nearest airport is not recommended.