diff --git a/pkg/assertoor/coordinator.go b/pkg/assertoor/coordinator.go
index e9f7999b..b725061a 100644
--- a/pkg/assertoor/coordinator.go
+++ b/pkg/assertoor/coordinator.go
@@ -366,10 +366,12 @@ func (c *Coordinator) runEpochGC(ctx context.Context) {
 		var sleepTime time.Duration
 
 		networkTime := time.Since(genesis.GenesisTime)
+		slotDuration := time.Duration(specs.SlotDurationMs) * time.Millisecond //nolint:gosec // G115: slot duration values won't overflow int64
+
 		if networkTime < 0 {
 			sleepTime = networkTime.Abs()
 		} else {
-			currentSlot := uint64(networkTime / specs.SecondsPerSlot) //nolint:gosec // G115: networkTime is checked non-negative above
+			currentSlot := uint64(networkTime / slotDuration) //nolint:gosec // G115: networkTime is checked non-negative above
 			currentEpoch := currentSlot / specs.SlotsPerEpoch
 			currentSlotIndex := currentSlot % specs.SlotsPerEpoch
 			nextGcSlot := uint64(0)
@@ -385,10 +387,10 @@ func (c *Coordinator) runEpochGC(ctx context.Context) {
 				select {
 				case <-ctx.Done():
 					return
-				case <-time.After(specs.SecondsPerSlot / 2):
+				case <-time.After(slotDuration / 2):
 				}
 
-				nextEpochDuration := time.Until(genesis.GenesisTime.Add(time.Duration((currentEpoch+1)*specs.SlotsPerEpoch) * specs.SecondsPerSlot)) //nolint:gosec // G115: epoch*slots product won't overflow
+				nextEpochDuration := time.Until(genesis.GenesisTime.Add(time.Duration((currentEpoch+1)*specs.SlotsPerEpoch) * slotDuration)) //nolint:gosec // G115: epoch*slots product won't overflow
 
 				c.log.GetLogger().Infof("run GC (slot %v, %v sec before epoch %v)", currentSlot, nextEpochDuration.Seconds(), currentEpoch+1)
 				runtime.GC()
@@ -402,7 +404,7 @@ func (c *Coordinator) runEpochGC(ctx context.Context) {
 				}
 			}
 
-			nextRunTime := genesis.GenesisTime.Add(time.Duration(nextGcSlot) * specs.SecondsPerSlot) //nolint:gosec // G115: slot number won't overflow int64
+			nextRunTime := genesis.GenesisTime.Add(time.Duration(nextGcSlot) * slotDuration) //nolint:gosec // G115: slot number won't overflow int64
 			sleepTime = time.Until(nextRunTime)
 		}
 
diff --git a/pkg/clients/consensus/blockcache.go b/pkg/clients/consensus/blockcache.go
index fe74bb37..d904f72f 100644
--- a/pkg/clients/consensus/blockcache.go
+++ b/pkg/clients/consensus/blockcache.go
@@ -19,6 +19,7 @@ import (
 )
 
 type BlockCache struct {
+	logger         logrus.FieldLogger
 	followDistance uint32
 
 	specMutex sync.RWMutex
@@ -56,6 +57,7 @@ func NewBlockCache(ctx context.Context, logger logrus.FieldLogger, followDistanc
 	}
 
 	cache := BlockCache{
+		logger:         logger,
 		followDistance: followDistance,
 		blockSlotMap:   make(map[phase0.Slot][]*Block),
 		blockRootMap:   make(map[phase0.Root]*Block),
@@ -145,6 +147,14 @@ func (cache *BlockCache) SetClientSpecs(specValues map[string]interface{}) error
 		return err
 	}
 
+	if specs.SlotDurationMs == 0 {
+		if secondsPerSlot, ok := specValues["SECONDS_PER_SLOT"]; ok {
+			if v, vOk := secondsPerSlot.(time.Duration); vOk {
+				specs.SlotDurationMs = uint64(v.Milliseconds()) //nolint:gosec // G115: SECONDS_PER_SLOT is always a small positive value
+			}
+		}
+	}
+
 	if cache.specs != nil {
 		mismatches := cache.specs.CheckMismatch(&specs)
 		if len(mismatches) > 0 {
@@ -185,7 +195,13 @@ func (cache *BlockCache) InitWallclock() {
 		return
 	}
 
-	cache.wallclock = ethwallclock.NewEthereumBeaconChain(cache.genesis.GenesisTime, specs.SecondsPerSlot, specs.SlotsPerEpoch)
+	if specs.SlotDurationMs == 0 || specs.SlotsPerEpoch == 0 {
+		cache.logger.Errorf("cannot initialize wallclock: neither SLOT_DURATION_MS nor SECONDS_PER_SLOT are available from the beacon API (SlotDurationMs=%d, SlotsPerEpoch=%d)", specs.SlotDurationMs, specs.SlotsPerEpoch)
+		return
+	}
+
+	slotDuration := time.Duration(specs.SlotDurationMs) * time.Millisecond //nolint:gosec // G115: slot duration values won't overflow int64
+	cache.wallclock = ethwallclock.NewEthereumBeaconChain(cache.genesis.GenesisTime, slotDuration, specs.SlotsPerEpoch)
 	cache.wallclock.OnEpochChanged(func(current ethwallclock.Epoch) {
 		cache.wallclockEpochDispatcher.Fire(&current)
 	})
diff --git a/pkg/clients/consensus/chainspec.go b/pkg/clients/consensus/chainspec.go
index 7de457cf..c855c2c5 100644
--- a/pkg/clients/consensus/chainspec.go
+++ b/pkg/clients/consensus/chainspec.go
@@ -25,7 +25,7 @@ type ChainSpec struct {
 	BellatrixForkEpoch   uint64         `yaml:"BELLATRIX_FORK_EPOCH"`
 	CappellaForkVersion  phase0.Version `yaml:"CAPELLA_FORK_VERSION"`
 	CappellaForkEpoch    uint64         `yaml:"CAPELLA_FORK_EPOCH"`
-	SecondsPerSlot       time.Duration  `yaml:"SECONDS_PER_SLOT"`
+	SlotDurationMs       uint64         `yaml:"SLOT_DURATION_MS"`
 	SlotsPerEpoch        uint64         `yaml:"SLOTS_PER_EPOCH"`
 	MaxCommitteesPerSlot uint64         `yaml:"MAX_COMMITTEES_PER_SLOT"`
 }