diff --git a/docs/docs/api.md b/docs/docs/api.md
index 64e26de8..986654a4 100644
--- a/docs/docs/api.md
+++ b/docs/docs/api.md
@@ -582,6 +582,14 @@ $ curl https://manifold.markets/api/v0/market -X POST -H 'Content-Type: applicat
                  "initialProb":25}'
 ```
 
+
+### `POST /v0/market/[marketId]/close`
+
+Closes a market on behalf of the authorized user.
+- `contractId`: Required. The id of the market to close.
+- `closeTime`: Optional. Milliseconds since the epoch to close the market at. If not provided, the market will be closed immediately. Cannot provide close time in past.
+
+
 ### `POST /v0/market/[marketId]/resolve`
 
 Resolves a market on behalf of the authorized user.
diff --git a/functions/src/close-market.ts b/functions/src/close-market.ts
index 86d73107..b8b252a7 100644
--- a/functions/src/close-market.ts
+++ b/functions/src/close-market.ts
@@ -9,16 +9,17 @@ import { APIError, newEndpoint, validate } from './api'
 
 const bodySchema = z.object({
   contractId: z.string(),
+  closeTime: z.number().int().nonnegative().optional(),
 })
 
 export const closemarket = newEndpoint({}, async (req, auth) => {
-  const { contractId } = validate(bodySchema, req.body)
+  const { contractId, closeTime } = validate(bodySchema, req.body)
   const contractDoc = firestore.doc(`contracts/${contractId}`)
   const contractSnap = await contractDoc.get()
   if (!contractSnap.exists)
     throw new APIError(404, 'No contract exists with the provided ID')
   const contract = contractSnap.data() as Contract
-  const { creatorId, closeTime } = contract
+  const { creatorId } = contract
   const firebaseUser = await admin.auth().getUser(auth.uid)
 
   if (
@@ -29,15 +30,22 @@ export const closemarket = newEndpoint({}, async (req, auth) => {
     throw new APIError(403, 'User is not creator of contract')
 
   const now = Date.now()
-  if (closeTime && closeTime < now)
+  if (!closeTime && contract.closeTime && contract.closeTime < now)
     throw new APIError(400, 'Contract already closed')
 
+  if (closeTime && closeTime < now)
+    throw new APIError(
+      400,
+      'Close time must be in the future. ' +
+        'Alternatively, do not provide a close time to close immediately.'
+    )
+
   const creator = await getUser(creatorId)
   if (!creator) throw new APIError(500, 'Creator not found')
 
   const updatedContract = {
     ...contract,
-    closeTime: now,
+    closeTime: closeTime ? closeTime : now,
   }
 
   await contractDoc.update(updatedContract)