diff --git a/frontend/model/contracts/group.js b/frontend/model/contracts/group.js
index 1d3ed9718d..1c08b834ce 100644
--- a/frontend/model/contracts/group.js
+++ b/frontend/model/contracts/group.js
@@ -14,7 +14,7 @@ import {
 import { paymentStatusType, paymentType, PAYMENT_COMPLETED } from './shared/payments/index.js'
 import { createPaymentInfo, paymentHashesFromPaymentPeriod } from './shared/functions.js'
 import { merge, deepEqualJSONType, omit, cloneDeep } from './shared/giLodash.js'
-import { addTimeToDate, dateToPeriodStamp, compareISOTimestamps, dateFromPeriodStamp, isPeriodStamp, comparePeriodStamps, dateIsWithinPeriod, DAYS_MILLIS } from './shared/time.js'
+import { addTimeToDate, dateToPeriodStamp, compareISOTimestamps, dateFromPeriodStamp, isIsoString, isPeriodStamp, comparePeriodStamps, dateIsWithinPeriod, DAYS_MILLIS } from './shared/time.js'
 import { unadjustedDistribution, adjustedDistribution } from './shared/distribution/distribution.js'
 import currencies from './shared/currencies.js'
 import { inviteType, chatRoomAttributesType } from './shared/types.js'
@@ -324,7 +324,7 @@ sbp('chelonia/defineContract', {
     periodStampGivenDate (state, getters) {
       return (recentDate: string | Date) => {
         if (typeof recentDate !== 'string') recentDate = recentDate.toISOString()
-        if (!isPeriodStamp(recentDate)) throw new TypeError('must be date or isostring')
+        if (!isIsoString(recentDate)) throw new TypeError('must be date or isostring')
         const { distributionDate, distributionPeriodLength } = getters.groupSettings
         if (!distributionDate) return
         const sortedPeriodKeys = getters.groupSortedPeriodKeys
@@ -349,7 +349,7 @@ sbp('chelonia/defineContract', {
           const waitingPeriodStamp = dateToPeriodStamp(
             addTimeToDate(distributionDate, -distributionPeriodLength)
           )
-          return recentDate >= waitingPeriodStamp ? waitingPeriodStamp : undefined
+          return recentDate >= dateFromPeriodStamp(waitingPeriodStamp) ? waitingPeriodStamp : undefined
         }
         const oldestKnownStamp = sortedPeriodKeys[0]
         const latestKnownStamp = sortedPeriodKeys[sortedPeriodKeys.length - 1]
@@ -375,7 +375,7 @@ sbp('chelonia/defineContract', {
         if (!distributionDate) return
         // This is not always the current period stamp.
         const distributionDateStamp = dateToPeriodStamp(distributionDate)
-        const sortedPeriodKeys = getters.groupSortedPeriodKeys
+        const sortedPeriodKeys = getters.groupSortedPeriodKseys
         const latestKnownStamp = sortedPeriodKeys[sortedPeriodKeys.length - 1]
         // Maybe the distribution date has just been updated,
         // but the corresponding period has not started or is not stored yet.
diff --git a/frontend/model/contracts/manifests.json b/frontend/model/contracts/manifests.json
index f833852102..4ea9eec712 100644
--- a/frontend/model/contracts/manifests.json
+++ b/frontend/model/contracts/manifests.json
@@ -1,7 +1,7 @@
 {
   "manifests": {
     "gi.contracts/chatroom": "21XWnNS9zeT2tws6KkJqkibLGfTivPdiGYbSjjqFEkDjL5Q775",
-    "gi.contracts/group": "21XWnNK3pmNAdgXLe7rkjVjEQ1z3Lccp3o7YpZ64bAr18VNPAW",
+    "gi.contracts/group": "21XWnNPBQsrLKSPxFX8kT5g2E9pym4q2gvnzfXp2T8zHfaNqKp",
     "gi.contracts/identity": "21XWnNN7wGNxzFZmiS4ft2TumavYYAgemSuFrGavTVJpxqtnyg",
     "gi.contracts/mailbox": "21XWnNHJ7MALCinR7vnu4GM82nq5DLhe6nhEDzruTuTw9CTnXP"
   }
diff --git a/frontend/model/contracts/shared/time.js b/frontend/model/contracts/shared/time.js
index 23484f201e..a5384dddc8 100644
--- a/frontend/model/contracts/shared/time.js
+++ b/frontend/model/contracts/shared/time.js
@@ -132,13 +132,17 @@ export function humanDate (
 }
 
 export function isPeriodStamp (arg: string): boolean {
-  return /\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}.\d{3}Z/.test(arg)
+  return isIsoString(arg)
 }
 
 export function isFullMonthstamp (arg: string): boolean {
   return /^\d{4}-(0[1-9]|1[0-2])$/.test(arg)
 }
 
+export function isIsoString (arg: string): boolean {
+  return typeof arg === 'string' && /\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}.\d{3}Z/.test(arg)
+}
+
 export function isMonthstamp (arg: string): boolean {
   return isShortMonthstamp(arg) || isFullMonthstamp(arg)
 }