It depends. If the lich knows how threatening the party is it might open with Time Stop, Gate, Wall of Force to buy some time to buff up while the party fights a balor or whatever the lich wants to call in. If the party is threatening but not worth the XP cost of a calling version of Gate, it can just use the Time Stop to buff up (provided it doesn't use some sort of divination every morning to find out whether it should cast any short-term buffs that day and if so when, or otherwise have information about exactly when the party will be showing up) or summon a bunch of minions with Summon Monster spells, or Create Greater Undead, or Symbol of Insanity, or Prismatic Sphere, or Mind Fog or other cloud conjurations that do nasty things... and that's just quickly browsing the PHB spell list.
Or a personal favourite of mine: Time Stop. Dimension Door out of Line of Sight of the party (but: within line of sight of where it was standing, more than True Seeing range away), Quickened Invisibility and Project Image of itself where it was standing the next round (this guarantees that the lich can pull it off within 2 rounds, which is the minimum duration of Time Stop). Take the skill trick from Complete Scoundrel that makes one spell "read" as another with spellcraft and have it seem to cast Mislead instead of Time Stop. True Seeing dude sees that it is only an illusion, confirming that Mislead was what was cast... but somehow the lich can't be seen with True Seeing. The party is likely to be confused by this tactic (if Mind Blank or Nondetection defeats True Seeing in your rules interpretation, that's what they are likely to assume has happened, provided they know about that interaction) and will probably (assuming they make their Spellcraft check) ignore the Projected Image for long enough that the Lich can buff up and then start taking the party on from the Projected Image.
Thanks - the lich has a lair, so the party will be engaged by some minions in the beginning, anyhow. Once the minions are engaged, the lich will be able to judge the party's strengths and buff up, when needed.
Good idea on foiling the True Seeing with the skill trick. Thanks!