If you don't mind me voicing an opinion on preparing spells - of course it's up to our DM, but:<br/>In 3.5, abandoning a spell to make room for another<em>does</em>require the wizard rest before spell preparation again, so that's not quick.<br/><br/>Interestingly, though I've never seen anyone do it, in 3.5 a wizard can leave spell slots empty, and fill these during the day as needed.  This requires preparation, but not additional rest.<br/><br/>The preparation of only a single spell (or of no more than 1/4 of one's daily capacity) takes 15 minutes.<br/><br/>(all from the SRD)<br/><br/>Now, SOH might of course call our unconscious time between shipwreck and waking on the beach "rest", but I doubt it's 8 hours... :)